na-adjective
Obsolete adjectival noun meaning odd or bizarre. Not used in modern Japanese; encountered only in historical texts.
古文書に「怪体なるものを見たり」とある。
An old document says, 'I saw a strange thing.'
Modern common word for 'strange' or 'odd'; 怪体 is its obsolete predecessor.
The exact derivation is uncertain; the kanji 怪 ('mysterious') and 体 ('form') suggest a historical compound meaning 'strange form'.