How many letters does the top answer for “reduced in strength or concentration or quality or purity” have?

The most common answer is dilute (6 letters).

Crossword clue: reduced in strength or concentration or quality or purity

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

dilute 6 letters wn-def

lessen the strength or flavor of a solution or mixture

diluted 7 letters wn-def

reduced in strength or concentration or quality or purity

a symptom of reduced quality or strength 50% similar → deterioration