stiff up
C1 informal inseparable intransitive
In simple words
To become hard and difficult to move, like your muscles after exercise.
Literal meaning: To become stiff.
Meanings
1 C1 informal
To become stiff or rigid, especially in the muscles or joints (non-standard variant of 'stiffen up').
"My knees always stiff up when the weather gets cold."
Grammar: inseparable
Usage notes
This form is non-standard and uncommon. Most native speakers prefer 'stiffen up.' It may appear in informal speech in some dialects. ESL learners are advised to use 'stiffen up' instead.
Commonly used with
muscles joints back neck
Forms
Base
stiff up
I/you/we/they
3rd person
stiffs up
he/she/it
Past simple
stiffed up
yesterday
Past participle
stiffed up
have + pp
-ing form
stiffing up
continuous
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