noun

• (uncountable, university slang, often capitalized) Clipping of chemistry (“branch of natural science”), usually referring to the subject or the department.
  "It boils down to science. Biology, chemistry and physics. I used to hate bio and chem. Now they fascinate me because I’ve realised they make up the world around us as well as us."
• (countable, informal, often in the plural) Clipping of chemical.
  "The seas, morosely fished by Ethan and the others, are heavily polluted, with Ethan informing Timothy, who risked a freezing dip: “If the tide doesn’t get you, the chems will. You want to stay healthy past forty, alive past fifty, you’ll remember to stay well out of the water.”"
• (countable, informal, often in the plural) Clipping of chemical.
  "This is the very opposite of what we’ve called for — namely, for Biden to publicly identify in advance a specific US (at least) hard-power response to Putin’s use of chems (or other weapons of mass destruction)."
• (countable, informal, often in the plural) Clipping of chemical.
  "“I actively searched for someone to tell me how they’d made an informed and calculated choice to use chems and, that for them, the chem scene is just recreation.” […] “Even those who told me sex on chems made them feel ‘like a don’ would follow up such celebratory statements with tales of rejection, regret, loneliness and longing for intimacy,” he said."

adj

• (informal) Clipping of chemical.
  "chem plant; chem weapons"