pull out all the stops
/ˈpʊl‿aʊt‿ɔːl ðə ˈstɒps/ verb
Forms pulls out all the stops pulling out all the stops pulled out all the stops pull out all stops
- verb (idiomatic) To hold back or reserve nothing. “They pulled out all the stops for the gala wedding.”
Synonyms
empty the tank give one's all go all out go balls to the wall go the whole nine yards go up to eleven open the floodgates
Etymology
An allusion to organ stops, which are pulled out to turn on each set of sounds in a pipe organ. When all stops are pulled out, the organ will play all variations of its sounds at once, therefore being as loud as possible.
Sources: Wiktionary — from the Wiktionary entry “pull out all the stops”, CC BY-SA 4.0. Details