knuckle - definition and synonyms

verb 

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/ˈnʌk(ə)l/
present tense
I/you/we/theyknuckle
he/she/itknuckles
present participleknuckling
past tenseknuckled
past participleknuckled

phrasal verbs

knuckle down

[intransitive]
present tense
I/you/we/theyknuckle down
he/she/itknuckles down
present participleknuckling down
past tenseknuckled down
past participleknuckled down
informal
to start working hard, especially when you should have done this earlier

It’s time you knuckled down to some work.

knuckle under

[intransitive]
present tense
I/you/we/theyknuckle under
he/she/itknuckles under
present participleknuckling under
past tenseknuckled under
past participleknuckled under
informal
to do what someone tells you to do

He wasn’t going to knuckle under to some woman.