Ground a child after reprieve on vacation (6)
I believe the answer is:
reason
'ground' is the definition.
('reason' can be a synonym of 'ground')
'a child after reprieve on vacation' is the wordplay.
'child' becomes 'son' (son is a kind of child**).
'after' is a charade indicator (letters next to each other).
'on vacation' means to remove the middle letters.
'reprieve' with its middle removed is 're'.
'a'+'son'='ason'
'ason' after 're' is 'REASON'.
(Other definitions for reason that I've seen before include "'Motivation, grounds (6)'" , "Justification; sanity" , "Motive for an action" , "Cause, justification" , "Justification needed" .)