Learn That Word

Synonyms for Weaken (same or very similar meaning)

WordNet sense 1 (destroy property or hinder normal operations):
counteract, sabotage, subvert, undermine, countermine

WordNet sense 2 (lessen in force or effect):
break, damp, dampen, soften

WordNet sense 3 (reduce the level or intensity or size or scope of):
de-escalate, step down

From the ODE community, based on WordNetadd/edit