WordWeb Online

1. Consider carefully and deeply; reflect upon; turn over in one's mind
    
2. Use or exercise the mind or one's power of reason in order to make inferences, decisions, or arrive at a solution or judgments
   "I've been cogitating all day and getting nowhere";
   - think, cerebrate

Derived forms: cogitated, cogitates, cogitating

Type of: chew over, contemplate, excogitate, meditate, mull, mull over, muse, ponder, reflect, ruminate, speculate, think over