usage: make strong or stronger; "This exercise will strengthen your upper body"; "strengthen the relations between the two countries"
2. fortify, fort, enclose, close in, inclose, shut in
usage: enclose by or as if by a fortification
3. arm, build up, fortify, gird
usage: 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"
4. fortify, add
usage: add nutrients to; "fortified milk"
5. spike, lace, fortify, change, alter, modify
usage: add alcohol to (beverages); "the punch is spiked!"