The Collaborative International Dictionary of English v.0.48:
onionskin \on"ion*skin`\, n. [Onion + skin.] A kind of thin but strong translucent paper with a glossy finish. [Webster 1913 Suppl.]WordNet (r) 3.0 (2006):
onionskin n 1: a thin strong lightweight translucent paper used especially for making carbon copies [syn: onionskin, flimsy]