IPA: /ˈwiːkli/
KK: /ˈwikli/
Not strong or powerful; lacking in physical strength or energy.
After the illness, she felt weakly and needed to rest.
Comparative: weaker
Superlative: weakest
In a manner that shows little physical strength or force.
He weakly protested against the decision.
Weakly → It is formed from "weak" (from Old English "wēac", meaning lacking strength) and "-ly" (meaning in a manner of). The word "weakly" means in a manner that lacks strength or force.
Think of someone acting in a way that shows they are 'lacking strength' — that's what 'weakly' means.