Just consider "another" as "an" plus "other". In other words, it is "an+other" and cannot be plural. That is the difference.

Randy has given you the perfect answer. 'Another' is simply the article indefinite article 'an' plus the 'other', written as one word instead of two. An + other = another So you use the word 'another' in exactly the same way that you use the article 'a' or 'an' - before singular countable indefinite nouns. An apple ---> another apple A man ---> another man A book --> another book You don't use it with plurals (other people) or with uncountable nouns (other information) or together with other determiners (my other sister, that other book, the other house).

another + singular noun other + plural noun I need another cup. (cup is singular so we use another) I need other cups. (cup is plural so we use other) :)