The Open Dictionary

rock-solid

adjective

UK/ˌrɒkˈsɒl.ɪd/
US/ˌrɑːkˈsɑː.lɪd/

Definitions of rock-solid adjective

  1. unlikely to move, break, or fail; extremely stable or reliable.

    • Their relationship is rock-solid, having stood the test of time.

    • The company's financial situation is rock-solid.

    • After thorough testing, the software's stability is rock-solid.