1. Nouns having two plural forms with different meanings

appendix – appendixes or appendices (for ‘medical terms’)
appendix – appendices (for addition/s to a book)

brother – brothers (for ‘sons of the same parent’)
brother – brethren (for ‘members of a society or a community’)

cloth – cloths (for ‘kinds or pieces of cloth’)
cloth – clothes (for ‘garments’)

die – dies (for ‘stamps for printing or coining’)
die – dice (for ‘small cubes used in games’)

index – indexes (for ‘tables of contents to books’)
index – indices (for ‘signs used in algebra’)

penny – pennies (for ‘number of coins’)
penny – pence (for ‘amount in value’)

2. Nouns having two meanings in the singular but one in the plural

light = radiance; light = a lamp
lights = lamps

people = nation; people = men and women
peoples = nations

powder = dust; powder = a dose of medicine in fine grains like dust
powders = doses of medicine

practice = habit; practice = exercise of a profession
practices = habits

3. Nouns having one meaning in the singular but two in the plural

colour = hue
colours = hues; colours = the flag of a regiment

custom = habit
customs = habits; customs = duties levied on imports

effect = result
effects = results; effects = property

ground = earth; ground = reason
grounds = enclosed land attached to house; grounds = reasons; grounds = dregs

letter = letter of the alphabet
letters = letters of the alphabet;  letters = literature

manner = method
manners = methods; manners = correct behaviour

moral = a moral lesson
morals = moral lessons; morals = conduct

number = a quantity
numbers = quantities; numbers = verses

pain = suffering
pains = sufferings; pains = care, exertion

premise = proposition
premises = propositions; premises = buildings

quarter = fourth part
quarters = fourth parts; quarters = lodgings

spectacle = a sight
spectacles = sights; spectacles = eye-glasses

4. Nouns having different meanings in the singular and the plural

advice =counsel
advices = information

air = atmosphere
airs = affected manners

amend = to change the words of a text, especially a law or a legal document; e.g. MPs were urged to amend the law to prevent another oil tanker disaster.
amends = to do something good to show that you are sorry about something you have done; e.g. I wanted to make amends for the worry I’ve caused you.

appearance = the way that someone or something looks
appearances = what things look like or seem to be rather than what they actually are; e.g. He was a far more complicated man than outward appearances suggested.

chain = i) a series of linked metal rings used for fastening or securing something, or for pulling loads; e.g. He slid the bolts on the front door and put the safety chain across.
ii) a sequence of items of the same type forming a line; e.g. He kept the chain of buckets supplied with water.
chains = a fact or situation that limits a person’s freedom

compass = extent, range
compasses = an instrument for drawing circles

damage = harm or injury; e.g. Strong winds had caused serious damage to the roof.  damages = money that is paid to someone by a person or organization who has been responsible for causing them some injury or loss; e.g. The police have been ordered to pay substantial damages to the families of the two dead boys.

force = strength
forces = troops

good = benefit, well-being
goods = merchandise/property

greeting = something friendly or polite that you say or do when you meet or welcome someone; e.g. They briskly exchanged greetings before starting the session.
greetings = a message that says you hope someone is well, happy, etc.; e.g.  birthday/Christmas greetings

humanity = i) people in general; e.g. Bombing civilians is a crime against humanity.
ii) understanding and kindness towards other people; e.g. If only he would show/display a little humanity for once. iii) the condition of being human; e.g. There is a sense of common humanity that unites people of all nations.
humanities = literature, language, history, philosophy, and other subjects that are not a science, or the study of these subjects

iron = a kind of metal
irons = fetters (बेड़ी(

pain = i) a feeling of physical suffering caused by injury or illness; e.g. These tablets should help to ease the pain. ii) emotional or mental suffering; e.g. The parents are still in great pain over the death of their child.
pains = to make a lot of effort to do something; e.g. I went to great pains to select the best staff available.

particular = special, or this and not any other; e.g. She wanted a particular type of bag.
particulars = details or information about a person or an event, especially when officially recorded; e.g. There’s a form for you to note down all your particulars.

proceeding = a particular action or course or manner of action
proceedings = i) a series of events that happen in a planned and controlled way; e.g. Millions of people watched the proceedings on television. ii) a complete written record of what is said or done during a meeting

physic = medicine
Physics = natural science

regard = i) to consider or have an opinion about something or someone; e.g. He is generally/widely regarded as the father of international law. ii) to look carefully at something or someone; e.g. The bird regarded me with suspicion as I walked up to its nest.
regards = i) Careful thought or attention; heed; e.g. She gives little regard to her sister’s teasing. ii) Respect, affection, or esteem; e.g. He has little regard for your work. iii) Good wishes expressing such sentiment; e.g. Give the family my best regards.

respect = regard
respects = compliments

return = i) to come or go back to a previous place; e.g. She left South Africa at the age of 15 and has never returned. ii) If people or things return to a previous condition, they go back to that condition; e.g. Within a week, the situation had returned to normal. iii) If you return to an activity or subject, you start doing it or talking about it again; e.g. Every five minutes, he returned to the same subject.
returns = goods that have been taken back to the shop where they were bought by customers because they are damaged or unsuitable

sand = a substance that consists of very small grains of rock, found on beaches and in deserts; e.g. Mix one part sand to three parts cement.
sands = large flat areas of sand near the sea; e.g. miles of golden sands

water = a colourless, transparent, odourless, liquid which forms the seas, lakes, rivers, and rain and is the basis of the fluids of living organisms. (पानी(
waters = i) the area of sea near to and belonging to a particular country; e.g. St Lucia depends on its clean coastal waters for its income. ii) the water contained in a particular lake, river, or part of the sea; e.g. In the shallow waters of the Gulf of Mexico, oil rigs attract fish.

way = a route, direction, or path; e.g. Do you know the way to the restaurant?
ways = structure consisting of a sloping way down to the water from the place where ships are built or repaired

wit = the ability to use words in a clever and humorous way
wits = intelligence and the ability to think quickly; e.g. She learned to survive on her wits.

wood = a hard substance that forms the branches and trunks of trees and can be used as a building material, for making things, or as a fuel; e.g. He gathered some wood to build a fire.
woods = an area of land, smaller than a forest, that is covered with growing trees