It is an inflection of Dim. It means to lessen the harmful effects of something, lessen, reduce, mitigate, wane, alleviate, weaken.
Dims is a verbal form of the transitive verb to attenuate. Specifically the 3. 3rd person singular of the present indicative. It means lessen or decrease the strength, intensity or value of something, an event, an expression or a misunderstanding.