1899, U.S. military slang for "Filipino" during the insurrection there, probably from a native word, or imitative of the babbling sound of their language to American ears (cf. barbarian). The term goo-goo eyes "soft, seductive eyes" was in vogue c.1900 and may have contributed to this somehow. Extended over time to "Nicaraguan," "any Pacific Islander" (World War II), "Korean" (1950s), "Vietnamese" and "any Asian" (1960s).
: Give it to the gook hospitals
An Asian or Polynesian; slope •Originally a Filipino insurrectionary, then a Nicaraguan, then any Pacific Islander during WWII, the term embraced Koreans after 1950, Vietnamese and any Asian fr 1960s; sometimes used of any colored person: take it on the chin better than an American or a Zulu or a gook/ the way he felt about Vietnam and the gooks/ It was there that I first heard of dinks, slopes, and gooks
[1900s+ Army; fr gugu, a term of Filipino origin, perhaps fr Vicol gugurang, ''familiar spirit, personal demon,'' adopted by US armed forces during the Filipino Insurrection of 1899 as a contemptuous term for Filipinos, and spread among US troops to other places of occupation, invasion, etc; probably revived after 1950 by the Korean term kuk, which is a suffix of nationality, as in Chungkuk, ''China,'' etc]