Guide always offers this thought (4)
I believe the answer is:
idea
'this thought' is the definition.
(idea is a kind of thought)
'guide always offers' is the wordplay.
'offers' says the answer is hidden in the clue (the clue holds or offers the answer).
'IDEA' is hidden in the letters of 'guide always'.
(Other definitions for idea that I've seen before include "Something imagined in the mind" , "Content of cognition" , "Theory" , "a wheeze" , "It comes to mind" .)