Source : WordNet®

hit the hay
     v : go to bed in order to sleep; "I usually turn in at
         midnight"; "He turns out at the crack of dawn" [syn: {go
         to bed}, {turn in}, {bed}, {crawl in}, {kip down}, {hit
         the sack}, {sack out}, {go to sleep}, {retire}] [ant: {get
         up}, {get up}]