Leader in being stern inspires the rest (8)
I believe the answer is:
breather
'rest' is the definition.
(breather is a kind of rest)
'leader in being stern inspires the' is the wordplay.
'leader in' indicates taking the first letters.
'stern' becomes 'rear' (rear of a ship).
'inspires' indicates putting letters inside (inspire means to breathe in).
The first letter of 'being' is 'b'.
'rear' placed around 'the' is 'reather'.
'b'+'reather'='BREATHER'
(Other definitions for breather that I've seen before include "Recovery time" , "A rest from work - rather be thus" , "An informal break - inhale and exhale" , "A rest - lung?" , "Short rest between bouts of exercise" .)