Definition of (even) a worm will turn in US English:

(even) a worm will turn

phrase

proverb
  • (even) a meek person will resist or retaliate if pushed too far.

    • ‘On one level, Heathcliff's ‘writhing’ allusion is clearly to the proverbial truth that, given sufficient provocation, ‘even a worm will turn’.’
    • ‘You know a worm will turn if it is trodden on?’
    • ‘‘Even a worm will turn,’ and now electricity and light, which have in the past gone to mathematics for solutions of their intricate problem, turn about and solve problems in mathematics which would require scores of years to complete.’
    • ‘He is exasperated and rushes upstairs to show his anger toward the child with the ice pick in his hand, screaming: ‘Even a worm will turn.’’
    • ‘Lady Ushant was as meek as a worm, but a worm will turn.’