Crikey! Etymology of expletive was one tough cuss. October 02, 2006 at 4:00 AM. Share ... Other sources say it’s a 19th century "minced oath," or mild-mannered cuss word, ...

A minced oath is a euphemism for words a speaker wants to avoid saying. The use of "darn" for "damn" or "gosh" for "God," are examples of minced oaths.

Incidentally, a minced oath is a euphemistic expression formed by replacing a term that could be deemed profane, blasphemous or taboo. For example, the common swapping of “God” with “gosh”.