According to OED (Third Edition, 2008), this word represents an aphetic form of Arabit, i.e. Arabic, also attested in English.
a.
gume rabite
1pharm.bot.gum Arabic, hardened sap of two types of acacia (used as a binding agent):
(
MS: 1250-1350
) Et tunc [...] distempera cum gleire u od gume rabite aparillé si: Pernez la gummam arabicam et pone en un drapel linge, et pone le drapel en ewe efforcié .i. teve
161rb
rabit (s.xiii-xiv)