The Twitter trademark

Within the Twitter guidelines on trademark: This document is designed to help you use our marks without having to worry about negotiating an agreement with us or talking to our lawyers.

Of the text: That said, "Tweet" means something specific and we aim to protect that meaning. , one notes that generic marks "mean something specific" [eg, thermos] but the ability to protect the trademark is gone.

See Lessons In Smart Trademark Management: Free Licensing Of The Mark From Twitter