What is a small one-masted vessel with mainsail and jib?
a dinghy would be a small (6 to 16 foot) sailboat, these can
have almost any sail rig. the type of rig you described is called a
sloop. a sloop is a sailboat with a triangular mainsail and a jib
(this sail configuration is called a marconi rig, or bermudian
rig), and are very common. so a small, one masted vessel with a
mainsail and jib would just be called a sloop, or dinghy.