Use 'ruminate' to describe intense or profound thought, often done silently and personally. She sat by the lake, ruminating on her life choices.
Pro Tip 2/3
Extended Thinking
'Ruminate' implies that thinking is spread out over time, not just a brief consideration. I need time to ruminate before making such a significant decision.
Pro Tip 3/3
Introspective Use
'Ruminate' is often used when thinking about one's feelings, actions or motivations. He ruminated on why he reacted so angrily at the meeting.