Singular and Plural Nouns

Normally the last word is made plural:

boy-friends break-ins travel agents

But where man and woman are prefixed both parts are made plural:

men drivers, women drivers

The first word is made plural with compounds formed of verb + er nouns + adverbs:

hangers-on, lookers-on, runners-up

and with compounds composed of noun + preposition + noun:

ladies-in-waiting, sisters-in-law, wards of court

Initials can be made plural:

MPs (Members of Parliament)

*VIPs (very important persons)

OAPs (old age pensioners)

UFOs (unidentified flying objects)