How many letters does the top answer for “register formally as a participant or member” have?

The most common answer is enrol (5 letters).

Crossword clue: register formally as a participant or member

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

enrol 5 letters wn-def

enroll 6 letters wn-def

recruit 7 letters wn-def