(ambitransitive) To (cause to) be no longer tense; to relax or loosen.
- 1977-1980, Lou Sullivan, personal diary, quoted in 2019, Ellis Martin, Zach Ozma (editors), We Both Laughed In Pleasure
It's incredible the wave of relaxation that has swept over me in the past few hours. Walking down the street, I didn't even have to concentrate on untensing in my facial muscles (which I realize are so often twisted up).