IPA: /ˈbɒksfəl/
KK: /bɑksfəl/
The amount of something that can fit inside a box.
She packed a boxful of toys to donate to the charity.
Boxful → It is formed from "box" (from Old English *box*, meaning a container or receptacle) and "-ful" (meaning full of). The word "boxful" means full of boxes or the amount that a box can hold.
Think of a box that is 'full of' something — that's what 'boxful' means.
No commonly confused words.