History (1300s-1960s)
There are several proposed origins of the word smut. According to the Oxford English Dictionary,[1] smut originated from the Middle English word smot, which had a similar meaning to its later definition – to smear or dirty. This form of smut comes from the 14th century. According to Etymonline, smut took on the meaning “indecent or obscene language” in the 1660s, which is closer to its modern use.
The later uses of smut, can be observed in the Ngram[2] of its usage in Google Ngram above. From 1934-1965, the word was used most frequently, and has since become more obscure. A search of books in this time period[3] smut reveals that it appeared most often in books about Smut Fungi.
[1] https://www.oed.com/dictionary/smut_v?tab=meaning_and_use&tl=true.
[3] https://www.google.com/search?q=\%22smut\%22&tbm=bks&tbs=cdr:1,cd_min:1934,cd_max:1965&lr=lang_en.