nebulous
adjective /ˈnebjələs/
/ˈnebjələs/
(formal)- not clear synonym vague
- a nebulous concept
Oxford Collocations DictionaryNebulous is used with these nouns:- concept
Word Originlate Middle English (in the sense ‘cloudy’): from French nébuleux or Latin nebulosus, from nebula ‘mist’. The current sense dates from the early 19th cent.