marrow

Etymology 1

From Middle English mary, marow, marwe, marowȝ, from Old English mearg, from Proto-West Germanic *maʀg, 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”), Polish mózg (“brain”), Persian مغز (mağz, “brain”).

noun

1. (uncountable) The substance inside bones which produces blood cells.
   Chop me up, I like to be hurt / Drink my marrow and blood for dessert 2004, Bloodbath, Eaten
2. (countable) A kind of vegetable like a large courgette/zucchini or squash.
   The finest European vegetables, cabbages, cauliflowers, potatoes, vegetable marrow, were lying in the market-hall, awaiting purchasers. 1847, Sir Robert Hermann Schomburgk, “Steam-Boat Voyage to Barbados”, in Bentley's Miscellany, volume XXII, London: Richard Bentley, page 37
3. The pith of certain plants.
4. The essence; the best part.
5. The inner meaning or purpose.
6. (medicine, colloquial) Bone marrow biopsy.
   This patient will have a marrow today.
7. (obsolete) Semen.

Etymology 2

From Old Norse margr.

noun

1. (Tyneside, informal) A friend, pal, buddy, mate.
   Cheers marrow!
2. (Scotland or archaic) One of a pair; a match; a companion; an intimate associate.
   The moon’s my constant Mistresse & the lowlie owle my morrowe. The flaming Drake and yͤ Nightcrowe make c. 1620, anonymous, “Tom o’ Bedlam’s Song” in Giles Earle his Booke (British Museum, Additional MSS. 24, 665)