She arrived yesterday. (She = one person - singular)
They are leaving soon. (They = more than one person - plural)
one day; two days
A church; two churches
A smash; two smashes
A bus; two buses
A ferry; two ferries
A lady; two ladies
A way; two ways
A play; two plays
Exceptions: i) Proper Nouns- the Kennedys
ii) Compounds ending with the preposition 'by'; layby laybys.
Nouns ending -o
Most can have either -os or -oes.
The following nouns take only -oes:
echoes; embargoes; goes; heroes; noes; potatoes; tomatoes; torpedoes; vetoes