set in stone

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set in stone

1. (idiomatic) Permanent; certain; firm.

   Synonyms: carved in stone, written in stone

   The decision won't be set in stone until we release the documents.

   • 2025 October 15, Vitali Vitaliev, “The recipe for Swiss bliss”, in RAIL, number 1046, page 68:

     So what is it that makes SBB (Swiss national railways) tick? In my humble opinion, two things. Firstly, a comprehensive and set-in-stone integrated timetable (incorporating trains, ferries, cable cars and buses, including the world-famous yellow 'post-autos'), compiled four years in advance and which gets tested twice before it becomes operational.

set in stone (third-person singular simple present sets in stone, present participle setting in stone, simple past and past participle set in stone)

1. (transitive, idiomatic) To render something permanent, certain, or firm.

   The plan looks good, but don't set it in stone until we have discussed it a bit more.