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.
yuck (2) Look up yuck at Dictionary.com
"laugh," 1938, yock, probably imitative.