How many letters does the top answer for “a syntactic string of words that forms a part of some larger syntactic unit” have?

The most common answer is syntagm (7 letters).

Crossword clue: a syntactic string of words that forms a part of some larger syntactic unit

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

syntagm 7 letters wn-def

a syntactic string of words that forms a part of some larger syntactic unit

syntagma 8 letters wn-def

a syntactic string of words that forms a part of some larger syntactic unit