I came across this word in the book I’m reading at the moment (A Fatal Inversion by Barbara Vine in case you’re interested). You can probably guess that it’s the opposite of ‘illicit’, a word I’d always assumed is unpaired (i.e. one that looks like it should have an opposite, but doesn’t – I wrote a blog post on this a while back, which you can read here). Because that’s the kind of thing I think about. What a loser.
Licit means ‘lawful’ and comes from the Latin word licitus, meaning ‘lawful, permitted, allowed’ which is where we also get ‘licence’ from. Its first use in print was in 1483, and then someone stuck an ‘il’ on it to make its opposite number around 19 years later (‘il’ as a prefix often appears at the start of words beginning with ‘l’ to change the meaning – think logical/illogical, literate/illiterate, legal/illegal, and so on). For some reason – maybe because us humans much prefer doing/writing about bad behaviour over the good stuff…? – illicit went on to be used much more regularly while licit fell by the linguistic wayside. I also found a source that said that in the 19th century licit was ‘condemned unjustly as an Americanism’, which might be another reason we stopped using it (because it seems we’re xenophobic as well as naughty).