Synonyms for strengthen

Verb

1. strengthen, beef up, fortify, change, alter, modify

usage: make strong or stronger; "This exercise will strengthen your upper body"; "strenghten the relations between the two countries"

2. strengthen, change

usage: gain strength; "His body strengthened"

3. tone, tone up, strengthen, exercise, work out

usage: give a healthy elasticity to; "Let's tone our muscles"