1 reflect, think, muse, ponder, study, ruminate, cogitate, contemplate, cerebrate, be lost in thought, be in a brown study:
Please don't interrupt me while I'm meditating.
2 Often, meditate on or upon. consider, contemplate, mull over, reflect on or upon, ponder on or over, chew over, plan, scheme, devise, design, conceive, frame, think up, have in mind:
She was meditating revenge, while I was meditating on how to discourage her.