@Eirikr: Personally I am inclined to treat もろともに as separate, since に is a morpheme that forms adverbs, not a morpheme that attaches to existing adverbs. —Suzukaze-c (talk) 08:43, 26 August 2021 (UTC)
- @Suzukaze-c: The particle に (ni) is just that -- a particle, and thus not part of the preceding word.
- Lemmings-wise, I don't see any monolingual JA dictionaries that treat もろともに (morotomoni) as a lexical item -- just もろとも (morotomo).
- We already have numerous entries for various terms where adverbial particle と (to) is optional -- pretty much any of the adverbs formed through reduplication or through addition of り (-ri) (and often gemination as well).
- We also have numerous entries for various adjectives that take -na in the adnominal and -ni in the adverbial. According to the KDJ entry at Kotobank, this word started out as a noun + -na adjective, taking the に (ni) in regular adverbial use. Then the adjectival sense receded, and the adverbial use lost the に (ni), possibly by reanalyzing the final とも (tomo) as the usual particle combination (which is probably what it was originally anyway), and this can already impart a kind of adverbial quality. The additional に (ni) does not appear so much in modern usage, and when it does, all it seems to do is accentuate the adverb-ness of the term. This seems like something better suited to a usage note than an entirely independent entry. ‑‑ Eiríkr Útlendi │Tala við mig 17:58, 26 August 2021 (UTC)