to become harder or more solid; to make arrangements more final and fixed
to become harder or more solid
Put the mixture somewhere cool to firm up.
firm sth up
to make arrangements more final and fixed
The company has not yet firmed up its plans for expansion.
to make sth harder or more solid
A few weeks of aerobics will firm up that flabby stomach.
Definitions from the Oxford Advanced Learner's Dictionary, 9th edition
