■ noun
1》 chiefly Brit. a vest or similar sleeveless garment.
2》 Physics a single line in a spectrum, not part of a multiplet.
3》 Physics a state or energy level with zero spin, giving a single value for a particular quantum number.
Origin
C18 (orig. denoting a man's short jacket): from single (because the garment was unlined) + -et 1 , on the pattern of doublet .