How many letters does the top answer for “pertaining to, or designating, a substance now called salicylal.” have?

The most common answer is spiroylic (9 letters).

Crossword clue: pertaining to, or designating, a substance now called salicylal.

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

spiroylic 9 letters web-def

Pertaining to, or designating, a substance now called salicylal. [Obs.]

spiroylous 10 letters web-def

Pertaining to, or designating, a substance now called salicylal. [Obs.]