'toasty' originates from English, specifically the word 'toast' plus the adjectival suffix '-y', where 'toast' ultimately comes from Latin 'tostare' meaning 'to roast'.

'toast' changed from Latin 'tostare' to Old French 'toster' (or similar forms) and Middle English forms such as 'tosten'/'tosten' and eventually became the modern English word 'toast'; the adjective 'toasty' was formed in English by adding '-y' to 'toast'.

Initially, the root meant 'to roast'; over time it came to mean 'bread or food browned by heat' and then extended to mean 'pleasantly warm' (giving rise to the adjective 'toasty').