break (your) back

informal

to put a lot of effort into doing something.

I'm not going to break my back working for £120 a week! (often + doing something)

• a fight for life
• a fighting chance
• a fig leaf
• a figment of imagination
• a figment of your imagination
• a figure of fun
• a fine kettle of fish
• a fine line
• a finger in every pie
• a firm hand on the tiller
• a fishing expedition
• a fish out of water
• a flash in the pan
• a flight of fancy
• a flight of fantasy
• a flight of imagination
• a flip-flop
• a fly in the ointment
• a fly on the wall
• a fool and his money are soon parted.
• a fool's errand
• a force to be reckoned with
• a foregone conclusion
• a four-letter word
• a frame of mind