gook.

First attested in the 1890s, US military slang in reference to Filipinos (in particular, it is defined in an 1893 citation in Slang and Its Analogues as referring to prostitutes who followed army camps; it is defined similarly in a 1914 work). The word was used for Nicaraguans during the US military occupation there in the 1910s, and for Haitians during the US invasion there, when Herbert Seligman noted in 1920 that "The Haitians … are nicknamed 'Gooks'". Other early uses in the 1920 and 30s still refer to people from the Philippines (a 1921 work refers to the Philippines as "Gook Land"), and the term also resembles goo-goo (“a Filipino person”), for which a variety of etymologies have been proposed; see that entry for more. (A later folk etymology suggests that during the Korean War, North Korean soldiers would shout Korean 美國 (Miguk, “America”) at Americans, who interpreted it as "me gook", as if identifying themselves as "gooks"; this ignores the many earlier examples of the word outside Korea.) Gook was used of Pacific Islanders by World War II, and Koreans and Vietnamese people by the time of the 1950s and 60s US military interventions there, which cemented the shift to meaning "Asian".

Possible blend of goop + gunk, or related to gobbledygook.

From the manner whereby a small child, still developing its speech, would mispronounce /l/ (spoken with the tip of the tongue behind the teeth) as /ɡ/ (spoken with the back of the tongue on the palate), which happens if one tries to say look without moving the tongue forward, thus requiring less effort to speak. Compare also wook and wike for “look” and “like”, in which cases the tongue is stationary and only the lips move.