IPA: //fækʌltəˈtɪvli//
KK: /fækʌltəˌtɪvli/
In a way that allows for choice or option; not mandatory.
The students can facultatively choose their projects based on their interests.
Facultatively → It is formed from "facultas" (meaning ability or power) and the suffix "-ively" (meaning in a manner of). The word "facultatively" means in a manner that allows for choice or ability, indicating an optional or discretionary nature.
Think of 'ability' ('facultas') to remember that 'facultatively' means something that is optional or based on one's choice.