Drip to turn lethargic (6)
I believe the answer is:
torpid
'lethargic' is the definition.
(synonyms)
'drip to turn' is the wordplay.
'turn' indicates an anagram.
'drip'+'to'='dripto'
'dripto' anagrammed gives 'TORPID'.
(Other definitions for torpid that I've seen before include "Inactive, dormant" , "Slow, dull" , "Inert" , "Lethargic, sluggish" , "Slow and apathetic" .)