Make a start, pave the way, as in Newton's theories broke the ice for modern physics. This idiom alludes to breaking ice in a channel so that a ship can pass. [Early 1600s] Also see break ground.

Relax a tense or very formal situation, as in Someone at the conference table will have to break the ice. [Early 1600s]

To remove the tension at a first meeting, at the opening of a party, etc.: “That joke really broke the ice at the conference; we all relaxed afterward.”