fortify

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

enclose by or as if by a fortification

prepare oneself for a military confrontation; "The U.S. is girding for a conflict in the Middle East"; "troops are building up on the Iraqi border"

add nutrients to; "fortified milk"

add alcohol to (beverages); "the punch is spiked!"