WordNet sense 1 (a thin strong lightweight translucent paper used especially for making carbon copies):

onionskin

WordNet sense 2 (very thin and insubstantial):

light

WordNet sense 3 (of relatively small extent from one surface to the opposite or in cross section):

thin

WordNet sense 4 (of low or inferior quality):

inferior

WordNet sense 5 (lacking solidity or strength and liable to break):

fragile

WordNet sense 6 (having little substance or significance):

slight, tenuous

WordNet sense 7 (having little physical or spiritual strength):

weak