General:
* Complete: This emphasizes finishing something.
* Saturate: This suggests filling something to capacity.
* Pack: This implies filling something tightly.
* Stuff: This is a more informal term for filling something.
* Populate: This suggests filling a place with people or things.
* Replenish: This implies refilling something that has been emptied.
Specific:
* Fulfill: This emphasizes meeting a need or requirement.
* Satisfy: This implies meeting a desire or need.
* Supplement: This implies adding something to something else to make it complete.
* Occupy: This suggests taking up space or time.
For specific situations:
* Fill in: To provide missing information.
* Fill out: To complete a form.
* Fill up: To make something full.
Please provide more context to get a more accurate synonym. For example, are you talking about filling a container, filling a role, or filling in information?