na-adjective, noun
Describes a person's disposition or temporary state of being too lazy to do something; often used in self-deprecating or critical remarks.
彼は気無精で、部屋の掃除をまったくしない。
He is so lazy that he never cleans his room.
今日は気無精が出て、何もする気が起きない。
I'm feeling lazy today and can't bring myself to do anything.
面倒くさい is an adjective meaning 'troublesome' or 'bothersome', focusing on the task being a hassle, whereas 気無精 describes the person's lazy disposition.
Compound of 気 (ki, 'spirit, mood') and 無精 (bushō, 'laziness, indolence'). The exact historical derivation is uncertain, but the word has been used since at least the Edo period to describe a lack of motivation or energy.