Nouns That Exist In Plural Form
Plural because of many parts – no singular
(i) Articles of dress having two inseparable pans: breeches, braces, drawers, pants, pantaloons, trousers, knickers, shorts, pajamas.
(ii) Instruments having two inseparable parts
bellows, compasses, nutcrackers, pliers, pincers, scissors, shears, snuffers, tongs, forceps
‘Forceps’ is a Latin noun and its Latin plural is ‘forcipes”. Its English plural was ‘forcepses’, but now ‘forceps’ is used as both singular and plural.
(iii) Diseases consisting of many parts (units, patches etc.)
measles, mumps, glands
They may be treated both as singular and plural.
Diseases like ‘chickenpox’, and smallpox’ were treated as plural formerly but now they are treated as singular.