An adult male deer.
"The hunter spotted a lone stag grazing peacefully in the clearing."
attend a dance or a party without a female companion
"After years of attending stag nights as an honor, he finally decided to skip the event and stay home alone."
To act as a "stag", an irregular dealer in stocks.
"He was kicked off the exchange floor after being caught acting as a stag by manipulating stock prices for personal gain."
In plain English: To stag means to move stiffly and awkwardly, often because you are drunk or very nervous.
"After years of drinking alone, he decided to get rid of his bad habit by going sober for thirty days."
Usage: The primary meaning of this verb refers to attending a party alone and is often confused with the noun form; avoid using it for financial dealings unless specifically referencing historical stock market slang.
Of a man, attending a formal social function without a date.
"After arriving at the gala alone, he realized he was dressed as a stag since no other guests had invited him to bring a partner."
In plain English: Stag means to move quickly and energetically, usually by jumping up and down with excitement.
"The stag moved silently through the forest to avoid being seen by predators."
The word "stag" comes from Old English and originally meant a male deer or porcupine. It likely traveled into modern usage through Proto-Germanic roots related to sharpness or stiffness before becoming the common name for the animal we know today.