swallow

The verb comes from Old English swelgan, from Proto-Germanic *swelganą, meaning to swallow, revel, or devour, tracing back to a Proto-Indo-European root meaning 'to gulp.' The bird sense is entirely separate, from Old English swealwe, from Proto-Germanic *swalwǭ, with no connection to the swallowing root at all.

The noun form of the 'gulp' word once meant a gulf, chasm, or whirlpool in Old English before narrowing to the act of swallowing itself. The bird's name, meanwhile, seems to have stayed fairly steady in meaning across its history.

The swallowing sense is kin to German schwelgen, meaning to delight or indulge, and to Dutch zwelgen, to revel or guzzle — suggesting old ideas of gulping and reveling were never far apart. It's also related to swill, from Old English swillan, to wash out or gargle.