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firm up

B1 neutral separable both
In simple words

To make a plan, deal, or body part stronger and more certain.

Literal meaning: To make something that is 'firm' go further in that direction — harder, more solid, more set.

Meanings

1 B1 idiomatic neutral

To make a plan, agreement, or arrangement more definite and certain.

"We need to firm up the details of the contract before the meeting on Friday."

"We need to firm up our plans for the summit."

— Reuters, diplomatic reporting, commonly attributed phrase in news coverage
Grammar: separable
2 B1 neutral

To become or make something physically harder or more toned.

"These exercises are designed to firm up your core muscles."

Grammar: separable
3 B2 idiomatic formal

To strengthen a position, relationship, or stance.

"The new trade agreement helped to firm up ties between the two countries."

Grammar: separable
Usage notes

Used both literally (muscles, physical objects) and figuratively (plans, agreements, relationships). Common in business and fitness contexts. Slightly more frequent in American English.

Commonly used with

plans deal muscles details agreement schedule

Forms

Base
firm up
I/you/we/they
3rd person
firms up
he/she/it
Past simple
firmed up
yesterday
Past participle
firmed up
have + pp
-ing form
firming up
continuous

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Synonyms

solidify finalize confirm tighten up cement nail down

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