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"reasoning" is also used as a crossword clue. If that's what you saw, the answer is often rationale (9 letters).
Definitions
endowed with the capacity to reason
Used in a sentence
“Her reasoning was clear and logical.”
“I don’t follow your reasoning on this issue.”
“Good reasoning helps solve complex problems.”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Logical thought”9 letters
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