This is a complicated word -- simple as it may look. Dialectal English chep, "piece of timber forming the sole of a turn-wrest plough; ‘the piece of wood on which the share is fixed'", appears to derive from French chep or cep, but is seemingly cognate with chip, which the OED derives from Latin cippus, but which lacks the sense of "share-beam" needed here. AND's gip appears to be a form of the same word. OED's supposition about a French etymon is borne out by FEW 2/i,692a's cep in the sense of "soc de la charrue" in Middle French, and more pertinently, DMF cep has the sense "pièce de bois supportant le soc de la charrue" which FEW gives only from modern dialects, and which is absent from both Gdf and TL. AND cep does not have the plough-related sense(s) either. The glossator's 'anglice' seems to confirm that in the case of gip, we are indeed, despite all of this, dealing with an M.E. word.