peacock

The 'pea' part traces back through Old English pēa/pāwa to Latin pāvō, borrowed from Ancient Greek taṓs, itself likely from a Pre-Greek source. The 'cock' part comes from Old English cocc, from Proto-West Germanic *kokk. Middle English pecok joined the two into one word.

What began as a Latin-derived word for the exotic bird itself (pāwa) got paired in Middle English with the everyday native word for a male fowl, cocc, to specify the male bird — giving rise to peacock, peahen, and peachick as a family set.

It's a cousin to peahen and peachick, which use the same 'pea-' element for the species with different endings marking sex or age; Old Norse páfugl, meaning 'peafowl,' shows the same Latin-derived root borrowed independently into another Germanic language.