IPA: /ɪɡˈzɔːstləsnəs/
KK: /ɪɡˈzɔstləsnəs/
The quality of being endless or having an unlimited supply.
The exhaustlessness of her energy amazed everyone around her.
Exhaustlessness → It is formed from "exhaust" (from Latin "exhaurire", meaning to draw out or drain) and "-less" (meaning without). The word "exhaustlessness" refers to the state of being without exhaustion or the quality of being inexhaustible.
Think of 'exhaust' meaning to draw out or drain, and '-less' meaning without — so exhaustlessness means being without the ability to be drained.