adverb taking the 'to' particle
Mimetic adverb describing the sound or action of swallowing something in one big gulp, often a drink.
He gulped down the beer in one go.
I swallowed the medicine with a gulp.
I was thirsty, so I gulped down the water in one swallow.
I swallowed the bitter medicine down in one gulp.
I was so nervous that my throat gave an involuntary gulp.