'grease' originates from Old English, specifically the word 'grǣs' (or Middle English 'gres'), where the root referred to animal fat or greasy substance.

'grease' changed from Old English 'grǣs' into Middle English 'gres' (and forms like 'grece'), and eventually became the modern English word 'grease' with senses of fat and lubricant.

Initially, it meant 'animal fat' or 'fatty substance', but over time it evolved to mean 'a lubricant' and then extended metaphorically to 'make something run smoothly' and to various slang senses.