Herdsman departs with dog (6)
I believe the answer is:
drover
'herdsman' is the definition.
(synonyms)
'departs with dog' is the wordplay.
'departs' becomes 'd' (abbreviation eg in train timetables).
'with' is a charade indicator (letters next to each other).
'dog' becomes 'rover' (Rover is a common name for a pet dog).
'd'+'rover'='DROVER'
(Other definitions for drover that I've seen before include "Rural worker" , "Person moving sheep or cattle from one place to another" , "One moving a herd or flock" , "I bring along many animals" , "One driving flock to market" .)