Moving or capable of moving at the highest speed; occurring in the shortest time possible.
From Old English 'fæst' meaning firm or fixed, which evolved to mean quick or rapid in Middle English. The superlative suffix '-est' was added to create the comparative form meaning 'most fast.'
Interestingly, 'fast' originally meant 'firmly fixed' rather than 'quick' - we still see this older meaning in phrases like 'hold fast' or 'fast friends.' The speed meaning developed because something moving quickly was seen as being 'close' or 'near' to its destination.
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