na-adjective, noun
self-indulgent; undisciplined; slovenly
Describes a person or lifestyle that is lazy, careless, and lacking self-control; often implies moral looseness or neglect of duties.
彼は自堕落な生活を送っている。
He leads a self-indulgent life.
自堕
You can't succeed with a negligent attitude.
怠惰 is a more formal term for laziness or indolence, often used in written or abstract contexts, whereas 自堕落 is more colloquial and carries a stronger connotation of self-indulgence.
Compound of 自 (self) and 堕落 (depravity, corruption). The exact historical derivation is uncertain, but the word likely emerged as a way to describe self-caused moral decline.