1
: having a sexual relationship with someone who is not your wife, husband, or partner
an unfaithful husband
—often + toShe has been unfaithful to him over the years. [=she has had sex with other people]
2
: not accurate
an unfaithful translation
—often + toThe movie was unfaithful to the book. [=the movie did not tell the story the way it was written in the book]
Cite this Entry
“Unfaithful.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/unfaithful. Accessed 22 Jun. 2026.
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