後退
こうたい · koutai · JLPT N1 · noun
retreat
後 (behind) + 退 (withdraw) = stepping back; the same sense gives backspace
Backspace moves the cursor back over typed text, so the retreat sense carries over to the delete key. 退 also appears in 退場, meaning exit from a stage or venue.
退 — walk radical 辶 + 艮 (stop/halt)
退 combines the walking/movement radical 辶 with 艮, which carries a sense of stopping or turning back. Together they depict the action of moving backward or withdrawing. The original sense of retreating or stepping back has remained stable through history.