IPA: /ˈɛf.ərt.ləs.nəs/
KK: /ˈɛfərtləsnəs/
The condition of doing something with ease and without any difficulty.
She completed the task with such effortlessness that it seemed like a breeze.
Effortlessness is formed from "effort" (from Old French *esforcier*, meaning to exert oneself) and "-lessness" (meaning without). The word describes a state of being without effort or exertion.
Think of 'effort' as the act of trying hard, and '-lessness' means without. So, effortlessness means being in a state where you don't have to try hard.