IPA: /dɪˈfɛns.ləs.nəs/
KK: /dɪˈfɛnsəsləsnəs/
The state of being unable to defend oneself; a lack of protection or strength against harm.
The defenselessness of the village made it an easy target for the invaders.
Defenselessness → It is formed from "defenseless" (from "defense" which comes from Latin "defensio" meaning protection, and the suffix "-less" meaning without) and the suffix "-ness" (meaning the state of being). The word "defenselessness" refers to the state of being without protection or defense.
Think of being 'without' ('-less') 'protection' ('defense') — that's why defenselessness means the state of being unprotected.