means The throwing back of light, heat, or sound from a surface, or — by extension — the act of thinking carefully and turning your own thoughts over in your mind.

from From Latin reflectere, "to bend back," built from re- ("back") and flectere ("to bend") — the same flexing root behind flexible and flex. It arrived in English through Old French in the late Middle Ages, first meaning light bending back off a surface, then bending inward to describe the mind doubling back on itself.