Marrow
Old English mearg, mærg (in marrow1 (sense 3 of the noun)), of Germanic origin; related to Dutch merg and German Mark . marrow1 (sense 1 of the noun) dates from the early 19th century.
wiktionary
From Middle English mary, marow, marwe, marowȝ, from Old English mearg, from Proto-Germanic *mazgą, *mazgaz, from Proto-Indo-European *mosgʰos. Compare West Frisian moarch, Dutch merg, German Mark, Swedish märg, Icelandic mergur, and also Russian мозг(mozg, “brain”), Persian مغز (mağz, “brain”).
From Old Norse margr.
etymonline
marrow (n.)
"soft tissue found in the interior of bones," late 14c., from Old English mearg "marrow," earlier mærh, from Proto-Germanic *mazga- (source also of Old Norse mergr, Old Saxon marg, Old Frisian merg, Middle Dutch march, Dutch merg, Old High German marg, German Mark "marrow"), from PIE *mozgo- "marrow" (source also of Sanskrit majjan-, Avestan mazga- "marrow," Old Church Slavonic mozgu, Lithuanian smagenės "brain"). Figurative sense of "inmost or central part, inner substance, essence" is attested from mid-14c.
