Etymology

Attested during the Edo period. Derived from でっぷり ‎(deppuri) with reduplication of the でぶ ‎(debu) element, in a similar pattern seen in other term pairs such as はっきり ‎(hakkiri) → はきはき ‎(hakihaki), ふらり ‎(furari) → ふらふら ‎(furafura), たっぷり ‎(tappuri) → だぶだぶ ‎(dabudabu), etc.

でっぷり ‎(deppuri) itself likely derives from 出っ張り ‎(deppari, “protruding”), from verb 出っ張る ‎(depparu, “to protrude”), a compound of prefixed verb 出る ‎(deru) ("to go out", used in a similar way to the English preposition out after a verb) and verb 張る ‎(haru) (of many meanings, the most relevant here being "to be taut / prominent / stuck out").