1530s, from assimilated form of in- (1) "not, opposite of" + reducible. Related: Irreducibly; irreducibility.
irreducible ir·re·duc·i·ble (ĭr'ĭ-dōō'sə-bəl, -dyōō'-)adj.
Impossible to reduce to a desired, simpler, or smaller form or amount.
Incapable of being made chemically simpler, or of being replaced, hydrogenated, or reduced in positive charge.