firm up

verb

1. To make (tentative plans) more definite.

   “Can we firm up plans for the barbecue Sunday?”

   “1977-1980, Lou Sullivan, personal diary, quoted in 2019, Ellis Martin, Zach Ozma (editors), We Both Laughed In Pleasure Just got a call from Falces office firming up my hospital date.”

2. To become more definite.

   “Let me know as soon as your plans firm up.”

3. To make (muscles) more toned through physical exercise.

   “He hopes to firm up his biceps a bit before meeting the girls.”

4. To become more toned through physical exercise.

   “After weeks of working out, his biceps finally began to firm up a bit.”

5. To become firmer in consistency.

   “Cook the omelet until the top has started to firm up.”