Husband aghast having to change label for topic

• Word prefaced by # used for online cross-referencing
• Symbol formed by four crossings in this puzzle
• One of 140 characters, often
• Symbol used in trend setting
• Word or phrase to aid online searches — hag's hat (anag)
• Online topic marker
• Social media feature - dice game for children
• It shares a key with a "3"
• Tweet symbol

Wikipedia Word definitions in Wikipedia
A hashtag is a type of label or metadata tag used on social network and microblogging services which makes it easier for users to find messages with a specific theme or content. Users create and use hashtags by placing the hash character (or pound sign) ...