WordNet sense 1 ((of words) formed in imitation of a natural sound):

echoic, onomatopoeic, onomatopoetic, onomatopoeical

WordNet sense 2 (constituting an imitation):

mimic

WordNet sense 3 (exhibiting mimicry):

mimetic

WordNet sense 4 (being or given to servile imitation):

apish

WordNet sense 5 ((often used in combination) not genuine but having the appearance of):

pseudo

WordNet sense 6 (constituting a copy or imitation of something):

mock

WordNet sense 7 (adopted in order to deceive):

sham

WordNet sense 8 (not genuine; imitating something superior):

counterfeit