What's shakin', BRO? is a phrase used as a friendly greeting, usually among young people. The crossword solutions for this phrase are BRO (3 letters), SUP (3 letters), and HIYA (4 letters). BRO is an abbreviation of brother, which is a term of endearment used to refer to a close friend. SUP is an abbreviation of what's up, which is another way of asking how someone is doing. HIYA is an informal way of saying hello.