completismEtymologyFrom complete + -ism. Originally from fanspeak, the slang of science fiction fans.completism means A desire to obtain a complete collection of some type of thing. Lexicurio rates it Sui generis — a strength score of 87 out of 100.nounA desire to obtain a complete collection of some type of thing.“A novel type of completism is Rothman's record and determination of attending every major convention held in this country.”