As much as the head or mind can hold or contain; a large amount of information or thoughts occupying one's attention.
Compound of 'head' and suffix '-ful' (full of); formed like other '-ful' words to indicate capacity, particularly mental capacity or confusion.
When someone has 'a headful,' you're imagining their brain as a container that's overstuffed—it's poetic because our brains actually ARE full of liquid and neural connections!
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