How can something be “defunct” when it was never “funct” in the first place? “Defunct” sounds like something that’s had the funk removed from it, like a freshly laundered pair of jeans or a Musak version of a James Brown song, but of course it means ‘no longer existing or functioning.’ It comes from Latin “defunctus” ‘dead,’ past participle of “defungi” ‘carry out, finish,’ from “de- “(expressing reversal) + “fungi” ‘perform.’ Aha. So it wasn’t “funct,” but it was “functioning,” which is from the same root.
“Fungible” always sounds to me like something that can be squeezed like a sponge, but it refers to goods or money ‘able to replace or be replaced by another equivalent item; mutually interchangeable.’ It also comes from “fungi” ‘perform,” as in the Latin phrase “fungi vice,” ‘serve in place of.’
“Perfunctory,” describes a slapdash, “lick and a promise” attempt to perform a duty. The Online Etymological Dictionary explains: ‘1580s, from L.L. perfunctorius “careless, negligent,” lit. “like one who wishes to get through a thing,” from L. perfungus, pp. of perfungi “discharge, get through,” from per- “through” + fungi “perform“’
Added note: I think it’s worth drawing attention to this comment from Steven Schwartzman of wordconnections.wordpress.com: “…although you accurately reported what the Online Etymological Dictionary says about perfunctory, that entry has a typo in it: the past participle of Latin perfungi was perfunctus, not perfungus, as I verified at