How many letters does the top answer for “the quality of being resistant to variation” have?

The most common answer is invariability (13 letters).

Crossword clue: the quality of being resistant to variation

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

invariability 13 letters wn-def

the quality of being resistant to variation

invariableness 14 letters wn-def

the quality of being resistant to variation

the quality of being subject to variation 60% similar → variability, variableness