Compound of classical Japanese 言 (*koto*, "speech, spoken thing") + 葉 (*ha/ba*, "leaf; blade"), the latter metaphorically extended to mean "unit of language." The leaf (葉) metaphor — individual words as leaves growing from the tree of speech — was already established in the *Man'yōshū* (8th century). Over time *kotoha* underwent sequential voicing (rendaku) of *h* → *b*, yielding modern *kotoba*.

Japanese culture places deep value on the power and weight of words; the concept *kotodama* (言霊, "word-spirit") holds that spoken words carry a living spiritual force that can affect reality. This belief underpins many Japanese social norms — speaking carefully, avoiding "unlucky" words at celebrations, and the preference for indirectness. When a Japanese speaker says "あの言葉が刺さった" ("those words pierced me"), it echoes this ancient sensitivity to *kotodama*.