From Longman Dictionary of Contemporary Englishslope off phrasal verb British English informalLEAVE A PLACEto leave somewhere quietly and secretly, especially when you are avoiding work Mike sloped off early today. → slope→ See Verb table
Examples from the Corpus
slope off• While the manager was away, Brian took the opportunity to slope off home an hour early every day.• "Where's Sam?" "I saw him sloping off to the pub half an hour ago." 