SEAR: To brown meat quickly by subjecting it to very high heat either in a skillet, under a broiler or in a very hot oven. The object of searing is to seal in the meat's juices, which is why British cooks often use the word "seal" to mean the same thing.
BRAISE: A cooking method by which food (usually meat or vegetables) is first browned in fat, then cooked, tightly covered, in a small amount of liquid at low heat for a lengthy period of time. The long, slow cooking develops flavor and tenderizes foods by gently breaking down their fibers. Braising can be done on top of the range or in the oven. A tight-fitting lid is very important to prevent the liquid from evaporating.
Lamb is normally cooked a little on the rare (pink inside) side.
ROAST: as a verb not a noun - To oven-cook food in an uncovered pan, a method that usually produces a well-browned exterior and ideally a moist interior. Roasting requires reasonably tender pieces of meat or poultry. Tougher pieces of meat need moist cooking methods such as braising
Don't know what cut of lamb you had - what kind of crust you were trying to develop .... or even why .... but I usually roast (on a rack) something like a leg of lamb without searing and it first (just a brushing of EVOO and a sprinkle of salt/pepper/rosemary) and it comes out with a nice crispy crust.
