Common words:
* flexible: capable of bending easily without breaking
* flexibility: the quality of being flexible
* flextime: a system of working hours that allows employees to choose their own starting and finishing times
* flexitarian: a person who follows a mostly vegetarian diet but occasionally eats meat
* flexor: a muscle that bends a limb or other part of the body
* flexion: the act of bending a limb or other part of the body
Less common words:
* flexibly: in a flexible way
* flexing: the act of bending or contracting a muscle
* flexure: a bend or curve in something
* flexuous: bending easily; supple
* flexile: easily bent or twisted
Slang and informal:
* flex: to show off or boast, especially about one's possessions or abilities
* flex on: to show off to someone
* flexing: the act of showing off
Let me know if you'd like to explore any of these words in more detail!