From A Wiki of Ice and Fire
Greyhound is a trading ship whose twin is Quicksilver. Their captains are brothers.
A Clash of Kings
At the port of Qarth the brother captains invite Daenerys Targaryen aboard Quicksilver to share Arbor red. Their price to book passage on Quicksilver or Greyhound is too high for her, however.
- ↑ 1.0 1.1 A Clash of Kings, Chapter 63, Daenerys V.