How many letters does the top answer for “the property being difficult or impossible to defeat” have?

The most common answer is indomitability (14 letters).

Crossword clue: the property being difficult or impossible to defeat

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

indomitability 14 letters wn-def

the property being difficult or impossible to defeat

invincibility 13 letters wn-def

the property being difficult or impossible to defeat

the property of being difficult to digest 50% similar → indigestibility