ぺこぺこ

Related to the verb 凹む (hekomu, “to become hollow or dented, to collapse inwardly, to sink in”).[1]

• (Tokyo) ぺ​こぺこ [péꜜkòpèkò] (Atamadaka – [1])[1] — specific to adverbial usage
• (Tokyo) ぺこぺこ [pèkópékó] (Heiban – [0])[1] — specific to adjectival usage
• IPA^(key): [pe̞ko̞pe̞ko̞]

ぺこぺこ • (pekopeko) 

1. (onomatopoeia) expressing the sound of thin metal as it dents and collapses: "plinkingly, tinkingly"

   缶(かん)がぺこぺこと凹(へこ)んだ。

   Kan ga pekopeko to hekonda.

   The can dented in with a plink.

2. (childish) expressing the idea of one's stomach collapsing inwards: "extremely hungrily"

   熊(くま)がぺこぺことゴミ箱(ばこ)の中(なか)で探(さぐ)りまわった。

   Kuma ga pekopeko to gomibako no naka de sagurimawatta.

   The bear hungrily groped around in the trash can.

3. humbly (see へこへこ)

   ぺこぺこと頭(あたま)を下(さ)げる

   pekopeko to atama o sageru

   to lower one's head humbly

• ぺこり (pekori)

ぺこぺこ • (pekopeko) -na (adnominal ぺこぺこな (pekopeko na na), adverbial ぺこぺこに (pekopeko ni ni))

1. extremely hungry

   ぺこぺこな時(とき)にどうする？

   Pekopeko na toki ni dō suru?

   What do you do when you're really hungry?