Part of a whole:
* Component
* Element
* Piece
* Section
* Unit
Person belonging to a group:
* Participant
* Associate
* Fellow
* Colleague
* Affiliate
* Adherent
* Supporter
Part of a body:
* Limb
* Appendage
* Organ
Other:
* Constituent
* Participant
* Actor
* Player
Example:
* "He is a member of the club." (Here, "participant" or "associate" would work)
* "The table has four members." (Here, "legs" or "components" would work)
To choose the best synonym, consider the specific context and the meaning you want to convey.