'smutty' originates from English, specifically the word 'smut' plus the suffix '-y', where 'smut' meant 'soot' or 'dirt'.

'smutty' changed from Middle English words such as 'smot'/'smut' (meaning 'soot, dirt') by addition of the adjectival suffix '-y', eventually becoming the modern English 'smutty'.

Initially it meant 'covered with soot or dirt', but over time it also acquired the sense of 'obscene or pornographic' (by extension from printed 'smut' meaning obscene material).