strengthen

verbs

make strong or stronger
"This exercise will strengthen your upper body"; "strengthen the relations between the two countries"
is derived from
is derived from
antonym
gain strength
"His body strengthened"
is derived from
antonym
is a type of (narrower)
undergo a change; become different in essence; losing one's or its original nature
"She changed completely as she grew older"; "The weather changed last night"
give a healthy elasticity to
"Let's tone our muscles"