a combining form occurring in loanwords from Greek, meaning “five” (Pentateuch); on this model, used in the formation of compound words (pentavalent).
A Long List of Affixes: Suffixes, Prefixes, and Combining FormsSuffixes -able, -ible, -ile: (form adjs) able to, fit to, worthy, capable; apt to; subject to being ~-ed -ac: one affect with -ac, -al, -ane, -ar, -ary, -ch, -ese, -ic, -ical, -id, -ile, -ine, -ish, -ory: like, of, pertaining to; characterized by -aceae: families of plants -aceous, -ous: resemblance to a substance; full of -acy, -age, -ance, -ancy, -asm, -dom, -ence, -ency, -hood, -ism, -ity, -ment, -mony, -ness, -ry, -ship, …
Also especially before a vowel, pent-.
Origin of penta-
< Greek pent-, penta-, comb. forms representing pénte five
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
fivepentagon; pentameter; pentaprism
Word Origin for penta-
from Greek pente five
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
word-forming element meaning "five, containing five," from Greek penta- (before a vowel pent-), comb. form of pente "five," related to Aeolian pempte (see five), with -a- by analogy of hepta-, ennea-, deka-.
Online Etymology Dictionary, © 2010 Douglas Harper
Containing five atoms, molecules, or groups:pentose.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.