Sublingual administration - will any mucous membrane do?

I note that according to wikipedia sub-lingual administration works by contact with the mucous membrane under the tongue. Could you also administer these drugs with more or less equivalent bioavaliability to using the under the tongue approach by using other mucous membranes (particularly intimate ones)?

Isn’t that how suppositories are supposed to work?

Yeah, suppositories and such. It’s also how snorting cocaine works. But if it’s not under the tongue, then it’s not sublingual because “lingual” means…?