See scales working as constant (9)
I believe the answer is:
ceaseless
'constant' is the definition.
(I know that constant can be written as ceaseless)
'see scales working' is the wordplay.
'working' indicates anagramming the letters.
'see'+'scales'='seescales'
'seescales' is an anagram of 'CEASELESS'.
'as' is the link.
(Other definitions for ceaseless that I've seen before include "Incessant, unremitting" , "Without end" , "Going on continually, incessant" , "Never-ending" , "Interminable" .)