definition of
strengthen

[1] #1 strengthen v. [beef up, fortify] make strong or stronger; "This exercise will strengthen your upper body"; "strengthen the relations between the two countries". wn

[2] #2 strengthen v. gain strength; "His body strengthened". wn

[3] #3 strengthen v. [tone, tone up] give a healthy elasticity to; "Let's tone our muscles". wn