noun

• (UK, Ireland, archaic) Bacon or fat, especially if with some remaining hair or bristles.
• (UK, Ireland, archaic) A roughly-cut or torn-off piece of bread or cheese.
  "But it is a braw elemental sphere this o' ours, for here's a good queich o' claret for ye, an' a shag o' butter-an'-bread."
• (often attributive) A deliberately messy, shaggy hairstyle.
  "There was that hair salon on Yonge Street called House of Lords. On a Saturday – nowadays you can't even imagine it – but imagine a hair salon having a lineup outside of people wanting to get a shag haircut."

verb

• (transitive) To make hairy or shaggy; to roughen.
  "He saw the pine its daring mantle rear, / Break the rude blast, and mock the brumal year / Shag the green zone that bounds the boreal skies, / And bid all southern vegetation rise."
• (intransitive, obsolete) To hang in shaggy clusters.
  "And long curld locks that downe his shoulders shag"

adj

• (obsolete) Hairy; shaggy.
  "Son. Thou liest, thou shag-hair'd villain!"

verb

• (intransitive) To shake, wiggle around.
• (UK, Ireland, transitive, slang, vulgar) To have sex with.
  "Every time since has been a disaster. Our sex life always has been. After k.b.ing me for ages, she’d eventually let me shag her."
• (UK, Ireland, intransitive, slang, vulgar) To have sex.
  "I'm not pregnant! I have shagged and shagged and shagged and all the little bastards missed!"
• (India, transitive, slang, vulgar) To masturbate.