Animal starts to rub himself in nut oil (5)
I believe the answer is:
rhino
'animal' is the definition.
(short for rhinoceros)
'starts to rub himself in nut oil' is the wordplay.
'starts to' says to take the initial letters.
The initial letters of 'rub himself in nut oil' is 'RHINO'.
(Other definitions for rhino that I've seen before include "Horned pachyderm" , "Horned beast (abbr.)" , "Powerful herbivorous odd-toed ungulate, informally" , "In brief, a large horned African animal" , "thick-skinned creature" .)