I'm not certain which word you are referring to as "blain" could have multiple meanings. Here are the two most common definitions:
Blain - a painful swelling or sore on the skin caused by inflammation or infection, also known as a blister or boil.
Blain - a Scottish or Northern English term meaning "to complain" or "to whine." It can also mean to express dissatisfaction or resentment.
If you have a different context or meaning in mind, please let me know and I'll be happy to provide a definition.