A ruler's working like a dream (7)
I believe the answer is:
surreal
'like a dream' is the definition.
(I've seen this before)
'a ruler's working' is the wordplay.
'working' indicates anagramming the letters.
'a'+'rulers'='arulers'
'arulers' is an anagram of 'SURREAL'.
(Other definitions for surreal that I've seen before include "RA rules (anag.)" , "Like a dream" , "Involving fantastical imagery" , "Bizarre, fantastic" , "Dreamlike; like Dali's art" .)