The change from bilabials and labiodentals F/v/p/b to m before n is a common development in many languages, no matter how "not … very likely" it seems to you. The mn then tends to simplify to m(m or n(n if there's no following vowel. Besides OHG Ram alongside Raban and Rabo for "raven", there's Westpfälzisch hann for standard High German haben "have", Icel. hrafn alongside hramn, "raven", or OE hræmn/hræm alongside hræfn, Latin somnus alongside sopor "sleep" and Danish søvn alongside Swedish sömn “sleep”. "n" following the labiodentals and bilabials is a difficult combination — either an intrusive vowel (as in Raban and English raven), or a nasalization to m occurs spontaneously. In the European languages the n seems to be part of an alternate n-stem declension of the root, and versions without this declension occur in some languages (e.g. Latin sopor and OHG Rabo — the alternate n-stem occurs with non-labial roots as well, without loss of the preceding consonant, e.g. OHG Aro and Arn, "erne/eagle").