not relevant; not applicable or pertinent

His lectures often stray to interesting but irrelevant subjects.

Law . (of evidence) having no probative value upon any issue in the case.

adjective

appropriate , necessary , pertinent , related , relevant

adjective

extraneous , foreign , garbage , immaterial , impertinent , inapplicable , inapposite , inappropriate , inappurtenant , inapropos , inapt , inconsequent , inconsequential , insignificant , not connected with , not germane , not pertaining to , off the point , off the topic , out of order , out of place , outside , pointless , remote , trivial , unapt , unconnected , unimportant , unnecessary , unrelated , without reference , extrinsic , heterogeneous , incidental , marginal , moot , nihil ad rem , nonessential , peripheral , tangential , unessential , wide of the mark