How many letters does the top answer for “making or having a sound as specified; used as a combining form” have?

The most common answer is sounding (8 letters).

Crossword clue: making or having a sound as specified; used as a combining form

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

sounding 8 letters wn-def

the act of measuring depth of water