To render something permanent, certain, or firm.

(archaeology, paleontology) A broad prehistoric period during which humans widely used stone for toolmaking. / (figuratively, informal) Any extremely primitive or undeveloped era.

A stone that can be stepped on in crossing something, especially a marsh or creek. / (idiomatic) Something used as a way to progress to something or somewhere else.

A stone set into the upper wall of Blarney Castle in Ireland, which if kissed is supposed to bestow the gift of the gab or blarney.

(idiomatic) Permanent; certain; firm.

any fruit with a soft fleshy exterior surrounding a hard pit or stone containing the seed / any plant in the genus Prunus

(medicine) A calculus in the kidney.

(alchemy, uncountable) A supposed substance able to turn base metals, such as lead or mercury, into gold or silver, also sometimes claimed to cure any illness (as panacea) or confer immortality (as elixir of life), among other functions.

Belonging in the Stone Age.

(UK, Australia, colloquial) Generalized expression of surprise or amazement, or just for emphasis.