The verb weaken has 5 senses (first 4 from tagged texts)
1. (6) weaken -- (lessen the strength of; "The fever weakened his body")
2. (2) weaken -- (become weaker; "The prisoner's resistance weakened after seven days")
3. (1) sabotage, undermine, countermine, counteract, subvert, weaken -- (destroy property or hinder normal operations; "The Resistance sabotaged railroad operations during the war")
4. (1) de-escalate, weaken, step down -- (reduce the level or intensity or size or scope of; "de-escalate a crisis")
5. dampen, damp, soften, weaken, break -- (lessen in force or effect; "soften a shock"; "break a fall")