My grandfather used the same term. His grandparents apparently had no alternative term, and they apparently brought it along in the covered wagon when they emigrated from western New York to Iowa in the 1850s. Grandpa's manner of speech was a strange thing, hard for me to quantify... it was a rural, middle-america hayseed thing with a curious sort of "Missouri" overlay, and some oddities from who knows where. I have never heard it pronounced exactly the same way by anyone in real life or film, and I don't think even I could do a fair imitation.
Anyway, along with a number of other admirable traits, he was remarkably free from some prevailing prejudices, but he had no "polite" terms for a great number of things. "That word" was a word like any other he had learned, not much different to him than referring to one car as a Studebaker and another as a Buick. As you mentioned, politically correct speech was nonexistent at that time and place.
Festus on Gunsmoke?