How many letters does the top answer for “an associate in an activity or endeavor or sphere of common interest” have?

The most common answer is cooperator (10 letters).

Crossword clue: an associate in an activity or endeavor or sphere of common interest

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

cooperator 10 letters wn-def

an associate in an activity or endeavor or sphere of common interest

pardner 7 letters wn-def

an associate in an activity or endeavor or sphere of common interest