Example : I mulled over the events of the afternoon.
Philosophers have speculated on the question of God for thousands of years.
The scientist must stop to observe and start to excogitate.

Synonyms : chew over, contemplate, excogitate, mull, mull over, muse, ponder, reflect, ruminate, speculate, think over

Example : He is meditating in his study.

Synonyms : contemplate, study