IPA: /fəˈtɪɡɪŋli/
KK: /fəˈtɪɡəˌlɪŋ/
In a way that causes tiredness or exhaustion.
The long meeting went on fatiguingly, leaving everyone exhausted.
Fatiguingly → It is formed from "fatigue" (from Old French *fatigue*, meaning weariness or tiredness) and the suffix "-ingly" (meaning in a manner that). The word "fatiguingly" describes something done in a manner that causes weariness or tiredness.
Think of the word 'fatigue' which means tiredness, and remember that 'fatiguingly' describes something that makes you feel tired.