Blimp's creator in the dumps (3)
I believe the answer is:
low
'in the dumps' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for low that I've seen before include "Not high or loud" , "Not elevated, may be base" , "something from Guernsey?" , "Deep sound of cattle - not high" , "Moo; not high" .)