yuck (2) Look up yuck at Dictionary.com
"laugh," 1938, yock, probably imitative.
yuck (1) Look up yuck at Dictionary.com
exclamation of disgust, 1966, origin perhaps echoic (compare Newfoundland slang yuck "to vomit," 1963; U.S. slang yuck "despised person," 1943; provincial English yuck "the itch, mange, scabies"). Variant yech is by 1969.