KNOWLEDGE[U, no plural]›knowledge about a subject, situation, etc or about how something works: We now have a better understanding of this disease.
AGREEMENT[C]›an informal agreement between two people: [usually singular, + that]We have an understanding that we don't discuss the subject in front of his mother.
SYMPATHY[U]›sympathy: Thank you for your understanding.
my/her/his, etc understanding›what you thought to be true: It was my understanding that she was coming alone.
ABILITY[U]›the ability to learn or think about something: The computer side of the course was way beyond my understanding (= was too difficult for me).