There are certain nouns that can be used in both singular and plural form. You can’t make plurals of these nouns by adding ‘s’ or ‘ies’. When they are used in singular sense they take singular verb, when they are used in plural sense they take plural verbs. Some of them are:

1. Miscellaneous

CRAFT = boat/boats. BARRACKS = a large building or group of buildings used to house soldiers. COUNSEL = barristers working in court. CROSSROADS = an intersection of two or more roads. ISSUE = children. OFFSPRING = children. WORKS = factory

1. a) That barracks is surrounded by a high wall.
b) All the three barracks were surrounded by a high wall.
c) All the police barracks of Delhi are old.

2. a) This is a dangerous crossroads.
b) Shilpa accelerated, seeing a crossroads ahead.
c) There are four dangerous crossroads on this stretch.

INCORRECT: All the aircrafts have to be checked and refuelled.
CORRECT: All the aircraft have to be checked and refuelled.

MEANS

The noun MEANS when refers to METHOD, it is, then, used either as singular or plural. But when it has the meaning of ‘wealth/source of income/monetary resources’ it is always plural; e.g.

a) Television is an increasingly important means of communication. (here MEANS = method)
b) This means is well known to all to do cheating to pass the examination. (here MEANS = method)
c) Several means of transport are available in this village. (here MEANS = method)
d) He succeeded by these means in passing the examination. (here MEANS = method)
e) His means are very small, but he has incurred no debt. (Here MEANS = wealth)
f) His means are insufficient to give him a good living. (Here MEANS = wealth)

2. Creatures

1. a) It’s very surprising that I have not seen a deer in this forest.
b) There are only two deer in this zoo.

2. a) He has only one sheep.
b) Why do you want to sell all your sheep?

3. Fish names