Singular and Plural - Important Words

1. The Compound Nouns are changed into Plural by changing the principal word :

Singular                        Plural                Singular                      Plural

brother-in-law               : brothers-in-law

commander-in-chief      : commanders-in-chief

looker-on                      : lookers-on

maid-servant                 : maid-servants

passer-by                       : passers-by

runner-up                      : runners-up

2. Some Nouns remain same in their both Singular and Plural forms :

Singular                        Plural                Singular                      Plural

furniture : furniture

deer : deer

Some other such words can be : aircraft, equipment, sheep, scissors, swine etc.

3. Many words have been adapted from other languages. Such words have their Plural forms according to their native usage as well as according to English usage. The foreign plural should preferably be used :

Singular                        Foreign Plural              English Plural

bureaus                         bureaux                               bureaus

criterion                         criteria                                criterions

curriculum                     curricula                           curriculums

datum                            data                                      datums

formula                         formulae                            formulas

index                             indices                                 indexes

lacuna                           lacunae                                lacunas

memorandum                memoranda                    memorandums

phenomenon                 phenomena                    phenomenons

syllabus                       syllabi              syllabuses