-d ə n adjective
Etymology: Middle English, from past participle of forbidden to forbid — more at forbid
1. : not allowed : not permitted : prohibited
the whole attraction of such knowledge consists in the fact that it is forbidden — Bertrand Russell
secretly enjoying a forbidden cigar
: taboo
forbidden meaning of a dream
2. : not conforming to the usual selection rules — used of quantum phenomena
forbidden transition
forbidden radiation
the line spectrum … would consist of only one line and be optically forbidden — L.M.Branscomb
• for·bid·den·ly adverb
• for·bid·den·ness noun -es