Tweetbot for Mac can hide usernames, hashtags, and keywords for a day, week, month, or forever (just like Tweetbot for iPhone and iPad). When you make a choice, Tweetbot for Mac then asks if you’d like to hide all appearances in your existing timeline. If you keep Tweetbot open for long periods of time, it collects hundreds of tweets, so this is useful for cleaning up your timeline in case you need to scroll or use ⌘-F to search it later.
Bonus Tip
You can share your keyword filters with fellow Tweetbot users.