(n.) Obsession of the mind in regard of a single subject only\; also, such a concentration of interest upon one particular subject or train of ideas to show mental derangement.

absorbed attention absorption application complex compulsion concentration contemplation deep study deep thought engagement engrossment fascination fixation fixed idea hang-up hypercathexis idee fixe immersion intentness involvement irresistible impulse meditation morbid drive obsession obsessive compulsion possession preoccupation prepossession profound thought rapt attention ruling passion single-mindedness studiousness study submersion tic