weaken become weaker; "The prisoner's resistance weakened after seven days"
modify,
alter,
change make less severe or harsh or extreme; "please modify this letter to make it more polite"; "he modified his views on same-gender marriage"
vitalise,
vitalize make more lively or vigorous; "The treatment at the spa vitalized the old man"
ruggedise,
ruggedize produce in a version designed to withstand rough usage; "Detroit ruggedized the family car"
substantiate solidify, firm, or strengthen; "The president's trip will substantiate good relations with the former enemy country"
strengthen -
gain strength; "His body strengthened"
weaken become weaker; "The prisoner's resistance weakened after seven days"
change 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"
consolidate make firm or secure; strengthen; "consolidate one's gains"; "consolidate one's hold on first place"
proof make resistant (to harm); "proof the materials against shrinking in the dryer"
back strengthen by providing with a back or backing
sandbag protect or strengthen with sandbags; stop up; "The residents sandbagged the beach front"
toughen make tough or tougher; "This experience will toughen her"
strengthen -
give a healthy elasticity to; "Let's tone our muscles"
