1.
starving; very hungry
Describes the feeling of being extremely hungry, with an empty stomach.
2.
bowing repeatedly; being obsequious
Describes the action of bowing repeatedly, often in an excessively flattering manner.
They bow obsequiously to important people, but act arrogant toward juniors.
ぺこぺこ is a mimetic word (擬態語) with two unrelated meanings.
SENSE 1 — HUNGRY:
- お腹がぺこぺこ: I'm starving
- Casual and friendly. Common among children and in everyday speech.
- Mimics the feeling of an empty, hollow stomach.
SENSE 2 — BOWING:
- ぺこぺこ頭を下げる: to bow repeatedly
- ぺこぺこする: to act obsequiously, to grovel
- Often has a negative nuance, implying excessive flattery or servility.
- Mimics the repeated up-and-down motion of bowing.
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Both senses are informal/colloquial. The hungry sense is particularly common in spoken Japanese.