I didn't see
arcanest in any dictionaries. Wiktionary is usually diligent about giving comparative and superlative forms, and it says
most arcane. This is backed up by the News on the Web corpus, that has no instances of
arcanest and about 100 of
most arcane. The most recent was from the
Guardian on 1 February:
The English planning system already has some of the most arcane rules about overlooking distances for new homes, making streets unnecessarily wide and windswept, and blocks placed needlessly far apart.
I think our word list can do without
arcanest - and
arcaner.
