From Longman Dictionary of Contemporary Englishfirm something ↔ up phrasal verb1 CERTAINLY/DEFINITELYto make arrangements, ideas etc more definite and exact We’re hoping to firm up the deal later this month.2 DSOEXERCISEto make a part of your body have more muscle and less fat by exercising → firm→ See Verb table
Examples from the Corpus
firm up• Jean Deleage and Guy Nohra will focus on health science firms.• The market was holding firm and edging up.• She moved with the motion of his hand, her firm stomach undulating up and down.• Now, however, there are worrying signs that the two biggest firms are ganging up on the rest.• The firm took up references on all the candidates interviewed.• Utah's economic planners want aerospace, bio-medical and computing firms to take up the slack.• Suppose a bank agrees to lend to a firm upon demand up to a certain amount.• A small cottage industry of biotechnology firms has sprung up to investigate this, using a variety of methods. 