Kipling's fourth poem on English existence (4)
I believe the answer is:
life
'existence' is the definition.
(life is a kind of existence)
'kipling's fourth poem on english' is the wordplay.
'kipling's fourth' becomes 'l' (4th letter of 'kipling').
'poem' becomes 'if' (I've seen this in other clues).
'on' is a charade indicator (letters next to each other).
'english' becomes 'e' (abbreviation).
'l'+'if'+'e'='LIFE'
(Other definitions for life that I've seen before include "Actuarial estimate of our remaining years" , ""But an empty dream" (Longfellow) - "As tedious as a twice-told tale" (Shakespeare)" , "Existence - biography" , "Animation" , "Maximum stretch?" .)