H21 or H-21 may refer to: British NVC community H21, a type of heath community in the British National Vegetation Classification Highway H21 (Ukraine) , a Royal Navy H-class submarine , a Royal Navy S-class destroyer Mata Hari (1876–1917), German spy code named H-21 Piasecki H-21, an American helicopter Institute H21, a Czech think tank that created the website Prezident 21
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).