Before I pass on, at the end, be especially ardent (10)
I believe the answer is:
passionate
'ardent' is the definition.
(similar in meaning)
'before i pass on at the end be especially' is the wordplay.
'before' means one lot of letters go next to another.
'end' indicates one should take the final letters.
'be especially' indicates an anagram.
The final letter of 'the' is 'e'.
'i'+'pass'+'on'+'at'='ipassonat'
'ipassonat' after 'e' is 'eipassonat'.
'eipassonat' anagrammed gives 'PASSIONATE'.
(Other definitions for passionate that I've seen before include "Ardent" , "Very keen" , "Showing strong emotions" , "Easily moved" , "enthusiastic" .)