How many letters does the top answer for “attempt by employing effort” have?

The most common answer is endeavor (8 letters).

Crossword clue: attempt by employing effort

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

endeavor 8 letters wn-def

a purposeful or industrious undertaking (especially one that requires effort or boldness)

endeavour 9 letters wn-def

earnest and conscientious activity intended to do or accomplish something

strive 6 letters wn-def

attempt by employing effort

make an effort or attempt 50% similar → essay, try