gack · interjection, verb, noun1
Apparently onomatopoeic and believed to have first appeared in comic strips. Compare gag (“to choke; to retch”) and hack (“to cough noisily”). The "cocaine" and "meth" senses apparently comes from the fact that snorting the drugs often activates a person's gag reflex.
gack · interjection, verb2
Apparently onomatopoeic. Compare German gack (“call of a hen”), German gackern (“(of a chicken) to loudly and repetitive cry”), and Dutch gakken (“(of a goose) to honk”). Comparison to more terms Pokorny compared German gackern to words including English gaggle, Latvian gâgát (“cry like a goose”), Russian gogotátь (gogotátʹ, “(of geese) cackle; laugh loudly”), Old Norse gaga (“mock, ridicule”), and Albanian gogësínj (“yawn, burp”), among others. Pokorny considered common origin or separate innovation both as possibilities to explain the similarities.
Etymology from Wiktionary, CC BY-SA 4.0.