(ˈ)pen.|tagən ə l, -taig- adjective
Etymology: Middle French, from Medieval Latin pentagonalis, from Late Latin pentagonum + -alis -al
1. : having five angles and five sides : five-sided : divided into pentagons
a pentagonal dodecahedron
2. : having a pentagon as section or base
a pentagonal column
a pentagonal pyramid
3. : relating or belonging to a pentagonal system
• pen·tag·o·nal·ly - ə lē - ə li adverb