Formal:
* Knowledgeable: This is a general term for someone who has a lot of knowledge about a particular subject.
* Informed: This implies that the person has access to and understands relevant information.
* Competent: This suggests that the person has the skills and abilities to understand and work with the subject.
* Expert: This is the highest level of understanding, indicating a deep and specialized knowledge.
* Proficient: This means the person is skilled and capable in a particular area.
Informal:
* Savvy: This implies practical understanding and awareness.
* Sharp: This suggests a quick and insightful mind.
* Bright: This is a general term for someone intelligent.
* On the ball: This implies someone who is aware and responsive to the situation.
* In the know: This means someone who has access to or understands insider information.
More specific terms:
* Astute: This suggests someone who is perceptive and insightful.
* Discerning: This implies someone who has good taste and judgment.
* Insightful: This means someone who has a deep understanding of the underlying reasons for something.
* Perceptive: This suggests someone who is aware of subtle details and nuances.
The best word to use will depend on the specific situation. For example, you might call someone "knowledgeable" about history, but "savvy" about technology.