Adjectives

(a)falsenot in accordance with the fact or reality or actuality“gave false testimony under oath”, “false tales of bravery”
(s)false, mistakenarising from error“a false assumption”, “a mistaken view of the situation”
(s)falseerroneous and usually accidental“a false start”, “a false alarm”
(s)falsedeliberately deceptive“false pretenses”
(s)delusive, falseinappropriate to reality or facts“delusive faith in a wonder drug”, “delusive expectations”, “false hopes”
(s)fake, false, faux, imitation, simulatednot genuine or real; being an imitation of the genuine article“it isn't fake anything; it's real synthetic fur”, “faux pearls”, “false teeth”, “decorated with imitation palm leaves”, “a purse of simulated alligator hide”
(s)falsedesigned to deceive“a suitcase with a false bottom”
(s)false, off-key, sourinaccurate in pitch“a false (or sour) note”, “her singing was off key”
(s)assumed, false, fictitious, fictive, pretended, put on, shamadopted in order to deceive“an assumed name”, “an assumed cheerfulness”, “a fictitious address”, “fictive sympathy”, “a pretended interest”, “a put-on childish voice”, “sham modesty”
(s)false, untrue(used especially of persons) not dependable in devotion or affection; unfaithful“a false friend”, “when lovers prove untrue”

Adverbs

(r)faithlessly, traitorously, treacherously, treasonably, falsein a disloyal and faithless manner“he behaved treacherously”, “his wife played him false”