IPA: /ˈdʒɑːrfəl/
KK: /dʒɑrˌfʊl/
The amount of something that can fit inside a jar.
She filled the jarful with cookies for the party.
Jarful → It is formed from "jar" (from Middle English *jarre*, meaning a container) and "-ful" (meaning full of). The word "jarful" means a quantity that fills a jar.
Think of a jar being 'full' — that's what 'jarful' means, a quantity that fills a jar.