Thought required in hide-and-seek? (4)
I believe the answer is:
idea
'thought' is the definition.
(I know that idea is a type of calculation)
'in hide-and-seek?' is the wordplay.
'in' says the answer is hidden in the clue.
'IDEA' can be found hidden inside 'hide and seek'.
'required' acts as a link.
(Other definitions for idea that I've seen before include "Inkling" , "Purpose" , "Product of the mind" , "It comes to mind" , "Notion, image" .)