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What is the difference between the following?

room's window
room's windows
rooms' window
rooms' windows

I'm mainly interested in the last two constructs.

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up vote 7 down vote accepted

room's window

A window belonging to a room.

room's windows

Multiple windows belonging to a room.

rooms' window

A window belonging to multiple rooms (probably a window connecting two rooms)

rooms' windows

Multiple windows belonging to multiple rooms

The plurality of windows distinguishes how many different windows there are.
The location of the apostrophe in rooms distinguishes how many different rooms there are.
's signifies that there is only one room and that room is in the genitive case.
s' should be thought of as rooms, with the apostrophe indicating it is in the genetive.

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My confusion was if rooms' window means one window per room or one window for all rooms. – Alexandru Nov 1 '10 at 0:48
@Alexandru Typically, one window for all rooms. – waiwai933 Nov 1 '10 at 1:03
I am curious, in the spoken form, would you pronounce the second 's on the last two? i.e. rooms-es – Anthony K Nov 1 '10 at 6:47
@Anthony K: room's and rooms' are pronounced the same, AFAICT. you'd have to figure it out from context – Claudiu Nov 1 '10 at 14:07
@Claudiu: That's correct. The only time you'd say "roomses" is if you meet a man named "Mr. Rooms" and you want to refer to his whole family, "The Roomses". Or if you're Sméagol from The Lord of the Rings. – Jon Purdy Nov 2 '10 at 4:04

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