How many letters does the top answer for “neglect or failure to perform.” have?

The most common answer is nonperformance (14 letters).

Crossword clue: neglect or failure to perform.

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

nonperformance 14 letters web-def

failure to act with the prudence that a reasonable person would exercise under the same circumstances

neglect or failure of communion. 50% similar → noncommunion

neglect or failure to fulfill. 50% similar → nonfulfillment

neglect or failure to pay. 50% similar → nonpayment