comp (n.) Look up comp at Dictionary.com
"complimentary ticket," 1885, short for complimentary. Meaning "nonpaying guest" is attested by 1930s; generalized to "anything given free" by 1960s. As a verb, by 1974. Related: Comped; comping. As a shortening of compensation (especially worker's/workman's) it was in use by 1970s.