firm up

Verb

firm up (third-person singular simple present firms up, present participle firming up, simple past and past participle firmed up)

1. (idiomatic, transitive) To make (tentative plans) more definite.
   • Can we firm up plans for the barbecue Sunday?
   • Just got a call from Falces office firming up my hospital date.1977-1980, Lou Sullivan, personal diary, quoted in 2019, Ellis Martin, Zach Ozma (editors), We Both Laughed In Pleasure
2. (idiomatic, intransitive) To become more definite.
   • Let me know as soon as your plans firm up.
3. (transitive) To make (muscles) more toned through physical exercise.
   • He hopes to firm up his biceps a bit before meeting the girls.
4. (intransitive) To become more toned through physical exercise.
   • After weeks of working out, his biceps finally began to firm up a bit.
5. (intransitive) To become firmer in consistency.
   • Cook the omelet until the top has started to firm up.