Thousands be troubled by dog (6,5)
I believe the answer is:
basset hound
'dog' is the definition.
(basset hound is a kind of dog)
'thousands be troubled' is the wordplay.
'troubled' indicates anagramming the letters.
'thousands'+'be'='thousandsbe'
'thousandsbe' is an anagram of 'BASSET-HOUND'.
'by' acts as a link.
(Other definitions for basset hound that I've seen before include "one that hunts, naturally" , "breed" , "Long-eared hunting dog" , "Sturdy hunting dog" .)