1. Characteristic of something that is very pleasant and self indulging: Steve and Margret stayed in a decadently luxurious hotel room complete with decadently delicious food that was served to them.
2. Relating to low morals and unrestrained desires for money to spend on all kinds of self-indulgent pleasures: There are those who criticize the very wealthy for decadently increasing their corruption and immorality for their personal benefits.