*mag-

late 15c., "to heap up for oneself," from Old French amasser "bring together, assemble, accumulate" (12c.), from à "to" (see ad-) + masser, from masse "lump, heap, pile" (from PIE root *mag- "to knead, fashion, fit"). Related: Amassed; amassing; amassable.

"in, in the midst of," early 12c., from Old English onmang, in late Old English sometimes amang, a contraction of ongemang "among, during," from the phrase on gemang, literally "in the crowd or company (of)," from on (see a- (1)) + gemengan "to mingle." Ths second element is from Proto-Germanic *mangjan "to knead together," which is perhaps from a nasalized form of PIE root *mag- "to knead, fashion, fit."

The collective prefix ge- was dropped 12c. leaving onmong, amang, among. Compare Old Saxon angimang "among, amid;" Old Frisian mong "among."