1) A fellow worker or partner.
The first example of its use is in a translated Latin text: 1365 ‘John de Roch` … says that on a certain day and year he made a pact with the said Richard [de Eltoft] that they should be partners for ploughing … with equal animals going in the plough, which partnership is called marows ’, Thorner
1530-1 Item to Christopher Falle and ys merro … for makyn the pentyse, xviijd, York. The word was also used in connection with teams of lead-miners: 1563 I do awe nootheyng … for I dedd pay trowelye for it when I dede take delyverans off ytt as ye headdeys man and is marrowys yt whrotthe ye grove dedd say ytt was, Grinton. It was used in an unpublished will of a pair of animals: 1662 to my daughter one quy which was marrow to the bull, Idle and in estate correspondence to draw a comparison between two deer: 1731 one spaved doe the marrow to this, Woodsome.