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"exhausting" is also used as a crossword clue. If that's what you saw, the answer is often tiring (6 letters).
Definitions
Very tiring or draining.
Word origin
From exhaust + -ing.
Used in a sentence
“This task is exhausting!”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Drains energy”10 letters
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