Superlative form of quick; the fastest or most rapid in speed or movement.
From Old English 'cwic' (alive, living), later meaning 'lively' and then 'fast.' The '-est' suffix creates the superlative form. The original sense of 'alive' evolved because living things move while dead things don't.
The phrase 'quicksand' preserves the original meaning—sand that's 'alive' or moving, even though quicksand isn't actually moving, showing how 'quick' started meaning alive, then fast, and the old sense stuck in compound words as a fossil.
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