THECA Meaning of THECA in English n. (pl. thecae) 1 Bot. a part of a plant serving as a receptacle. 2 Zool. a case or sheath enclosing an organ or organism. thecate adj.[ L f. Gk theke case ] Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012