means The highest point of a mountain, or the topmost level of anything — including a high-stakes meeting between leaders at the peak of power.

from From Old French 'somet,' a diminutive of 'som' meaning 'top' or 'highest part,' which traces back to Latin 'summum,' the neuter of 'summus' — 'highest.' So a summit is literally 'the topmost little bit.' The political sense, leaders meeting at the highest level, is a 20th-century extension — the figurative peak borrowed from the literal one.