Related Clues:

• Adam, Hoss and Little Joe on 'Bonanza'?
• "brb" or "ttyl"
• 'brb' or 'ttyl'
• TTYL or TTFN
• Message such as "LOL"
• Often-brief message
• Use thumbs, perhaps
• Sort of cell-phone message
• Send a written message by phone
• Word with book or box
• Send an emoji, say
• Sessions with a teacher
• Thumb-typist's message
• Helpful or distracting thing when studying
• Send a message in it, extraordinarily