molecule molecule /ˈmɑːləˌkjuːl/

noun

1. () (physics and chemistry) the simplest structural unit of an element or compound  ( molecule )
   (physics and chemistry) the simplest structural unit of an element or compound
     A water molecule consists of two hydrogen atoms bonded to an oxygen atom.
   A water molecule consists of two hydrogen atoms bonded to an oxygen atom.
   
2. (nontechnical usage) a tiny piece of anything  ( atom , corpuscle , molecule , mote , particle , speck )
   (nontechnical usage) a tiny piece of anything
     The scientist observed the movement of particles under a microscope.
   The scientist observed the movement of particles under a microscope.