General synonyms:
* Idea
* Notion
* Conception
* Opinion
* Belief
* Reflection
* Cogitation
* Contemplation
* Consideration
Synonyms emphasizing a specific aspect of thought:
* Process: Thinking, reasoning, deliberation, pondering, musing
* Result: Conclusion, judgment, decision, realization
* Content: Concept, theory, hypothesis, principle, proposition, belief, opinion
* Origin: Inspiration, insight, intuition
The best synonym will depend on the specific meaning you want to convey. For example, "He had a sudden thought" could be replaced by "He had a sudden realization" or "He had a sudden insight."
Let me know if you have a specific sentence or context in mind, and I can help you choose the most suitable synonym!