stickler
nounUK /ˈstɪk.lər/
US /ˈstɪk.lɚ/
A stickler is a person who insists very firmly that things be done exactly right.
My teacher is a stickler for neat handwriting.
RELATED WORDS
OTHER MEANINGS
2. A person who insists on strict adherence to rules or details.
He's a stickler for the rules and never lets anything slide.
3. A difficult problem or puzzling question.
That last crossword clue was a real stickler.
4. Something that causes difficulty or delay.
The missing signature proved a stickler for the whole deal.