Why do we say `five star hotel’ and not `five stars hotel’?

This is because `star’ is functioning as an adjective, and not as a noun. You can say that you saw `Five stars shining in the sky.’ But when a noun like hotel follows the word `star’, you say, `I had dinner in a three star hotel’. You do not say, `three stars hotel’. Similarly, you say, `I want five rupees’. But when the word `rupees’ is followed by the noun `coin’ or `note’, you say, `I need a five rupee coin/note’. You do not say, `five rupees note’. Joggers talk about a `twenty-mile marathon’, and not a `twenty miles marathon’.

Noun : Number

Singular Noun Definition:  When a noun means one only, it is said to be singular.
Examples:  boy, girl, book, church, box
Plural Noun Definition:  When a noun means more than one, it is said to be plural.
Examples:  boys, girls, books, churches, temples
Rule #1
The plural of nouns is usually formed by adding - s to a singular noun.
Exercise:  Write the plural of each of these nouns



Rule #2
Nouns ending in s, z, x, sh, and ch form the plural by adding - es.
Special Note:
If you add - s to such nouns as fox, bush, and bench, you will find that you cannot pronounce them without making an additional syllable.  This is why such nouns form the plural by adding - es.


Rule #3
Nouns ending in - y preceded by a consonant is formed into a plural by changing - y to - ies.  But this has exception, see rule #4 for that.
Examples:  lady, ladies; city, cities; army, armies

Rule #4
Nouns ending in y preceded by a vowel form their plurals by adding - s.
Example:  boy, boys; day, days



Rule #5
Most nouns ending in o preceded by a consonant is formed into a plural by adding es.  Example:  hero; heroes; grotto, grottoes

*may add - s or - es


Special Note:
Most nouns ending in o preceded by a vowel is formed into a plural by adding - s.
Example:  folio, folios; cameo; cameos; studio, studios; portfolio, portfolios

Rule #6
Some nouns ending in f or fe are made plural by changing f or fe to - ves.
Example:  beef, beeves; wife, wives

The following form their plurals by adding - s.

chief, chiefs	fife, fifes	mischief, mischiefs	hoof, hoofs
roof, roofs	grief, griefs	kerchief, kerchiefs	safe, safes

IRREGULAR PLURALS

man, men	foot, feet	mouse, mice
woman, women	tooth, teeth	louse, lice
child, children	ox, oxen	goose, geese

The following nouns have no singular:

scissors	oats	tongs	dregs
trousers	pinchers	bellows	snuffers
cattle	shears	measles	mumps
victuals	tweezers	vespers

Some nouns are always singular.  Some of these nouns may be used in the  plural when different kinds are meant as sugars, coffees, cottons

gold	silver	wheat	corn
molasses	copper	sugar	cotton

Singular nouns use this and that.
Plural nouns use these and those.

Collective nouns

There are vast range of collective nouns, some are used for many animals or groups like herd, while some are specific to particular group.
So lets first look at the common nouns, common to many groups:
herd - herd can be used of all grass eating animal groups mainly, eg. cattle, elephant, asses, buffalo, caribou ( a type of reindeer) ,

troop - baboon, apes, dogfish ( a dogfish is a small bottom-dwelling shark with a long tail)

colony - auk ( a short winged seabird) , beavers, ant, badgers ( a mammal from weasel family) , bats,