Fire off Definition 1 of 3Pro Tip 1/3Immediacy Conveys urgency of sending something without delay. As soon as the news broke out, the reporter fired off a tweet. Pro Tip 2/3Multi-tasking Suggests doing this quickly amidst other activities. Can you fire off those invites while I finish cooking? Pro Tip 3/3Casual Tone Not typically used in formal communication; more casual. I'll just fire off an SMS to let them know we're late.