See how fast father is! (4)
I believe the answer is:
time
'see' is the definition.
The answer and definition can be both related to thinking as well as being verbs in their base form.
Perhaps they are linked in a way I don't understand?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for time that I've seen before include "It's measured by watch or clock" , "Continuum of past, present and future" , "Spell" , "Duration; tempo" , "Prison sentence; occasion" .)