Crossword clue: a species of inflorescence; a dense panicle, as in the lilac and horse-chestnut.
1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
a dense flower cluster (as of the lilac or horse chestnut) in which the main axis is racemose and the branches are cymos