I came across "untactful" in a story and wondered when it was first used and how it came to be commonly used in speech. I've always used "tactless".
I checked a lot of dictionaries with no results. I searched for "origins of untactful" and "etymology of untactful" with no results.
I had no trouble finding the information about "tactless". It was first recorded in 1840–50 but had no luck with "untactful".
Google Stats - infers that "untactful" is new:
- "untactful" = About 547,000 results
- "tactless" = About 1,480,000 results