General synonyms:
* Conceive: To form an idea or plan in your mind.
* Envision: To imagine something in detail, especially something in the future.
* Visualize: To create a mental picture of something.
* Dream: To imagine something that is not real.
* Fantasize: To imagine something that is pleasant or exciting.
* Daydream: To imagine something pleasant while you are awake.
More specific synonyms:
* Conceptualize: To form an idea or concept.
* Visualize: To form a mental image of something.
* Hypothesize: To suggest an explanation for something.
* Speculate: To think about something in a tentative or uncertain way.
* Conjecture: To guess about something.
* Presume: To assume something is true without proof.
The best word to use will depend on the specific context. For example, if you are talking about creating a new product, "conceptualize" might be a good choice. If you are talking about imagining a future event, "envision" might be more appropriate.