'Sediment' is Latin for 'a settling' — from 'sedere' (to sit). Particles that 'sit down' in liquid.
Matter that settles to the bottom of a liquid; material deposited by water, wind, or glaciers.
From Latin 'sedimentum' (a settling, a sinking down), from 'sedēre' (to sit, to settle), from PIE *sed- (to sit). This root is among the most prolific in Indo-European, producing an extraordinary range of descendants: Latin 'sella' (seat, via *sed-la), 'sēdēs' (seat, abode), 'subsidium' (support, literally 'sitting in reserve'), 'praesidēre' (to preside, to sit before); Greek 'hédra' (ἕδρα, seat, base, as in 'cathedral'); Old English 'sittan' (to sit); Sanskrit 'sīdati' (he sits). The word captures
Sedimentary rocks — formed from compressed sediment — make up roughly 75% of the rocks exposed at the Earth's surface, yet only about 5% of the Earth's crust by volume. Nearly all fossils are found in sedimentary rock, because the gentle settling process that forms sediment is what buries and preserves organic remains. The etymological connection between 'sitting