Honey badger's length adding to value (5)
I believe the answer is:
ratel
'honey badger's' is the definition.
(synonyms)
'length adding to value' is the wordplay.
'length' becomes 'l' (abbreviation in geometry).
'adding to' says to put letters next to each other.
'value' becomes 'rate' (both can mean to esteem).
'l' after 'rate' is 'RATEL'.
(Other definitions for ratel that I've seen before include "One eats honey" , "Badger-like creature" , "Badger-like mammal" , "Musteline mammal" , "Honey badger" .)