As a proper noun scutum
is (constellation) a small autumn constellation of the northern sky, said to resemble a shield it lies between the constellations of aquila, sagittarius, and the tail of serpens.
As an adjective schtum is
(historical, Roman antiquity) An oblong shield made of boards or wickerwork covered with leather, with sometimes an iron rim; carried chiefly by the heavy-armed infantry of the Roman army.
(zoology) A scute.
(zoology) One of the two lower valves of the operculum of a barnacle.
(obsolete) A penthouse or awning.