A knave of the first rate: a phrase borrowed from the dyehouse, where certain colours are said to be in grain, to denote their superiority, as being dyed with cochineal, called grain. Knave in grain is likewise a pun applied to a cornfactor or miller.
KNAVE IN GRAIN
Meaning of KNAVE IN GRAIN in English
Slang English vocab. Английский сленговый словарь. 2012