A dream I think a lot about (7)
I believe the answer is:
reverie
'a dream' is the definition.
(I know that reverie is a type of dream)
'i think a lot about' is the wordplay.
I cannot really understand how this works, but
'i' is found in the answer.
'about' could be 're' ('re' means regarding or about) and 're' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for reverie that I've seen before include "Daydream or fantasy" , "Aimless train of thought" , "I revere being in a state of dreaminess" , "Wool-gathering" , "Daydream or preoccupation" .)