verb (used with or without object), down·vot·ed, down·vot·ing.
  1. to cast a vote against (an online comment, article, etc.) by clicking on an arrow or other icon, usually affecting the post's rank or position on a website.
  1. such an unfavorable vote.

Origin of downvote

First recorded in 2005–10; down1 + vote Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018