IPA: /ˈklɒzɪtˌfʊl/
KK: /ˈklɒzɪtˌfʊl/
The amount of items that can fit inside a closet.
She had a closetful of clothes that she never wore.
The word 'closetful' is formed from 'closet' (from Middle English *closet*, meaning a small room or cupboard) and '-ful' (meaning full of). Therefore, 'closetful' means full of closets or the contents of a closet.
Think of a 'closet' being 'full' — that's what 'closetful' means, something that is full of the items typically found in a closet.