cogitate

ˈkɒdʒɪteɪt

verb

think deeply about something; meditate or reflect.

he stroked his beard and retired to cogitate

think (about),contemplate,consider,give thought to,give consideration to,mull over,meditate (on),muse (on),ponder (on/over),reflect (on),deliberate (about/on),ruminate (about/on/over),dwell on,brood (on/over),agonize (over),worry (about),chew over,puzzle (over),speculate about,weigh up,revolve,turn over in one’s mind,review,study,be in a brown study,put on one’s thinking cap,pore on,cerebrate