The Collaborative International Dictionary of English v.0.48:
Irrepressible \Ir`re*press"i*ble\, a. Not capable of being repressed, restrained, or controlled; as, irrepressible joy; an irrepressible conflict. --W. H. Steward. [1913 Webster]WordNet (r) 3.0 (2006):
irrepressible adj 1: impossible to repress or control; "an irrepressible chatterbox"; "uncontrollable laughter" [syn: irrepressible, uncontrollable]