Dictionary.com
definitions

avirulent

[ey-vir-yuh-luh nt, ey-vir-uh-]

adjective

(of organisms) having no virulence, as a result of age, heat, etc.; nonpathogenic.

Origin of avirulent

First recorded in 1895–1900; a-6 + virulent
Related formsa·vir·u·lence, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for avirulent

avirulent

adjective

(esp of bacteria) not virulent
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
avirulent in Medicine

avirulent

[ā-vîr′yə-lənt, ā-vîr′ə-]

adj.

Not virulent.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.