(n.) Mental labor.

abstract thought act of thought application boning brainwork cerebration cogitation conceit conception conceptualization conning contemplation cram cramming creative thought drill engrossment excogitation exercise extensive study grind grinding heavy thinking idea ideation imageless thought inspection intellection intellectual exercise intellectualization lucubration mental act mental labor mental process mentation noesis perusal practice ratiocination reading reasoning restudy restudying review straight thinking study studying subject swotting thinking thinking aloud thinking out thought wide reading