grease [ME] The ultimate source of grease is Latin crassus ‘thick or fat’, and in medieval English the word meant ‘the fat part of the body of an animal’ and ‘fatness’. To grease someone’s palm, a phrase that dates from the early 16th century, is to bribe them. The metaphor comes from the idea of applying grease to a machine to make it run smoothly. The idea behind like greased lightning [M19th], ‘very quickly’, is that lightning, the fastest thing imaginable, would presumably be even faster if greased. See also glib.