"Patronize" often implies a more benign or well-intentioned form of superiority. For example, if someone is "patronizing" towards someone else, they may be doing so in an effort to be kind or helpful, but still have an underlying sense of superiority. It can also refer to the act of supporting or being a customer of a business or organization. "Condescend," on the other hand, has a more negative connotation and implies a more overt or intentional act of belittling or treating someone as inferior. It suggests an attitude of looking down upon someone, and can be seen as insulting or offensive. Overall, "patronize" is a milder form of condescension, while "condescend" carries a stronger negative connotation.

Both come from Latin words. The Latin root in "patron" means "father", it is someone who takes care of you. The Latin root in "condescend" means "climb down" or "descend", so it means descending to your level. That explains the difference.

"Patronize" is often used as a verb. It can mean to give a store your business, for example. Where these two words are similar is in their adjective forms. There the difference is really subtle. When someone is "patronizing" toward someone else, they act overly nice because they feel superior. When someone is "condescending", they talk down to others out of a sense of superiority. They might talk really slowly, use simple words, feel like they need to explain basic concepts, etc.

‘Patronizing’ has an at least ostensibly positive intention that ‘condescension’ doesn’t have.