[more contagious; most contagious]
1 : able to be passed from one person or animal to another by touching
a contagious disease
It's a highly contagious virus.
2 : having a sickness that can be passed to someone else by touching
I have a cold and I'm still contagious.
I'm sick, but the doctor says I'm not contagious.
3 : capable of being easily spread to others : causing other people to feel or act a similar way
She has a contagious smile. [=her smile makes other people smile; her smile makes other people happy]
— contagiously adverb
— contagiousness noun, [noncount]