I was recently looking up the etymologies of some obscure words related to the English word tribe (like the adjective tribual), and I came across a Wiktionary page that asserts that there is or was a Latin adjective "tribālis" meaning "tribal". The page even lists an (automatically generated, to be sure) "Classical" pronunciation, and says that English "tribal" and Italian "tribale" are "descendants" of Latin tribalis.
But I haven't been able to find evidence aside from this Wiktionary page of "tribalis" being a word in Latin. I checked the PHI Latin Texts corpus and Lewis and Short's dictionary, and it doesn't occur in these resources. The Oxford English Dictionary says that English "tribal" is from English tribe + -al, and does not mention any Latin "tribalis". There does seem to be a Latin adjective tribuarius that is derived from tribus. Since tribus is a 4th-declension/u-stem noun, I would be a bit surprised by the formation of "tribalis": it seems to me that the result of affixing -alis would be expected to be "tribualis".
Because of these considerations, I'm feeling fairly skeptical about the Wiktionary page. (The talk page of the user who created the entry seems to indicate that this user may have a bit of a pattern of adding entries for dubious Latin adjectives.) Has "tribalis" ever been used in Latin? If so, when and by whom? If not, I'd be interested in knowing if there any actually attested Latin -alis adjectives that drop the -u- from the stem of a related noun.