Bear to rub in with difficulty (5)
I believe the answer is:
bruin
'bear' is the definition.
(I've seen this before)
'rub in with difficulty' is the wordplay.
'with difficulty' is an anagram indicator.
'rub'+'in'='rubin'
'rubin' anagrammed gives 'BRUIN'.
'to' acts as a link.
(Other definitions for bruin that I've seen before include "Conventional name for a bear" , "Archetypal name for a bear" .)