IPA: /ˈnʌtˌɡɔl/
KK: /nʌtɡɔl/
A growth on a tree, especially an oak, caused by certain wasps that looks like a nut.
The nutgall on the oak tree was large and round, indicating a strong infestation.
Nutgall is formed from "nut" (from Old English *cyning*, meaning a hard-shelled fruit) and "gall" (from Old English *gealla*, meaning bile or gall). The term refers to a growth on oak trees that resembles a nut and contains a bitter substance, similar to gall.
Think of a 'hard-shelled fruit' ('nut') that has a 'bitter substance' ('gall') — that's why nutgall refers to a growth on trees that looks like a nut and has a bitter quality.
No commonly confused words.