How many letters does the top answer for “another word for relentlessness” have?

The most common answer is inexorability (13 letters).

Crossword clue: another word for relentlessness

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

inexorability 13 letters gen-syn

mercilessness characterized by an unwillingness to relent or let up

inexorableness 14 letters gen-syn

mercilessness characterized by an unwillingness to relent or let up

another word for about 50% similar → approximately, roughly, some

another word for terms 50% similar → footing

another word for under 50% similar → nether

another word for word 50% similar → phrase