D defs.my
Entry 2 senses Webster, 1913

Penta-

· Pen·ta- · IPA /pɛntə-/
01 pref. A combining form denoting five; as, pentacapsular; pentagon.
  1. 1.
    A combining form denoting five; as, pentacapsular; pentagon.
  2. 2.
    Denoting the degree of five, either as regards quality, property, or composition; as, pentasulphide, containing five sulfur atoms; pentoxide, containing five oxygen atoms, etc. Also used adjectively.(Chem.)