A shortage of twisted thread (6)
I believe the answer is:
'a shortage' is the definition.
(dearth can mean a shortage or lack)
'twisted thread' is the wordplay.
'twisted' is an anagram indicator.
'thread' is an anagram of 'DEARTH'.
'of' is the link.
(Other definitions for dearth that I've seen before include "Lack of resources" , "Severe lack" , "Shortage, paucity" , "Severe shortage" , "Scarcity, paucity" .)