Use the adjective molecular to describe something that has to do with or is made up of molecules. If you're studying molecular biology, you're focusing on the molecules that make up living things.

When a scientist studies things on a molecular level, she's looking at them up close, examining their cells. The adjective molecular comes up most often in biology and chemistry, and it always describes the very smallest units that make up organisms or elements. Molecular comes from the noun molecule, which means "extremely minute particle," from the Latin molecula, "tiny mass."

Definitions of molecular
  1. adjective
    relating to or produced by or consisting of molecules
    molecular structure”
    molecular oxygen”
    molecular weight is the sum of all the atoms in a molecule”
  2. adjective
    relating to simple or elementary organization
    “"proceed by more and more detailed analysis to the molecular facts of perception"--G.A. Miller”
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    pertaining to large units of behavior
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