What's the difference between 懒惰 and 懒?
懒 (lazy) is mainly an adjective (less often as a noun) 


Example:

懒人 (lazy person)

人懒 (the person is lazy)


  懒惰 (lazy/ laziness) can be an adjective or a noun. 


Example: 

由于他懒惰，他的花园里充满了杂草 (Due to he being lazy, his garden is full of weeds )

由于他的懒惰，他的花园里充满了杂草 (Due to his laziness, his garden is full of weeds )


  The adjective 懒惰 preceding a noun usually requires the adjectival prefix '的'  


Example: 懒惰的人 (lazy person)


  The adjective 懒惰 after a noun doesn't require adjectival prefix '的'


Example:人懒惰 (the person being lazy)