IPA: /ˈfiːb.lər/
KK: /ˈfiblər/
Less strong or less powerful than something else; weak.
After the illness, he felt feebler than before.
Feebler → It is formed from "feeble" (from Old French *feeble*, meaning weak or frail) and "-er" (meaning one who or more). The word "feebler" means one who is weaker or more frail than another.
Think of someone who is 'weaker' ('feeble') and the '-er' indicating a comparison. This helps you remember that 'feebler' refers to someone who is more weak.