'Concrete' is Latin for 'grown together into a solid mass' — from 'crescere' (to grow).
Existing in a material or physical form; not abstract; a building material made from cement, sand, gravel, and water; to cover with concrete.
From Latin 'concrētus,' past participle of 'concrēscere' (to grow together, to harden, to condense, to solidify), composed of 'con-' (together, with) + 'crēscere' (to grow, to arise, to increase). The PIE root is *ḱerh₃- (to grow). The word literally means 'grown together' — matter that has condensed or solidified from separate particles into a unified, indivisible mass. The philosophical use of 'concrete' versus 'abstract' derives from this physical image: concrete things are those that have 'grown together' into tangible, palpable form, while abstract things have been 'drawn away' (Latin 'abstractus') from physical
The building material 'concrete' got its name in 1834 because it is literally stuff that has 'grown together' — cement binding sand and gravel into a unified solid. But the abstract adjective came first by four centuries: philosophers were calling ideas 'concrete' (as opposed to 'abstract') long before anyone poured a sidewalk.