pentatomic

from The Century Dictionary.

• Containing in a single molecule five atoms altogether of the same or of different elements, as stannic chlorid, SnCl₄; or, containing in a single molecule five atoms of some one element, as a pentose, which is an aldehyde alcohol or a ketone-alcohol containing five atoms of carbon. Frequently used in the same sense as quinquevalent.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Having five atoms in the molecule.
• adjective Having five hydrogen atoms capable of substitution.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective chemistry Having five atoms in each molecule
• adjective chemistry Having five hydrogen atoms capable of substitution.