How many letters does the top answer for “serving as an essential component” have?

The most common answer is cardinal (8 letters).

Crossword clue: serving as an essential component

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

cardinal 8 letters wn-def

(Roman Catholic Church) one of a group of more than 100 prominent bishops in the Sacred College who advise the Pope and

fundamental 11 letters wn-def

the lowest tone of a harmonic series

key 3 letters wn-def

metal device shaped in such a way that when it is inserted into the appropriate lock the lock's mechanism can be rotated