- The historical figure Gautama Buddha, the founder of the Buddhist religion (when capitalized Buddha).
- A person who has achieved buddhahood, roughly meaning englightenment.
There are no categorical synonyms for this word. However, one could loosely refer to an englightened person or an arahant/arhat as synonyms.
Alternatively, in the context of Gautama Buddha, one could use any of the other generally accepted names as synonyms, e.g., Siddhārtha Gautama, Shakyamuni, Enlightened One, Awakened One, etc.
