adj.
Pronunciation: -sh ə s
Function: adjective
Date: 1542
1 a : capable of causing infection <viruses and other infectious agents> b : communicable by infection <an infectious disease> ― compare CONTAGIOUS
2 : that corrupts or contaminates
3 : spreading or capable of spreading rapidly to others <their enthusiasm was infectious > <an infectious grin>
– in · fec · tious · ly adverb
– in · fec · tious · ness noun