slighten

verb3

1. •
   To make or become slight; make or become less pronounced, less noticeable, or less obvious.

   • His smile slightened as if he knew they talked of him. — 2004
2. •
   To slight.

   • […] as God forbid that anyone should hint a slightening word of what our sons and brothers are doing just now, and doing for us! — 1920
3. •
   To level out, smooth, or flatten.