asymptomatic

Short definition from Wiktionary

Adjective

1. 1
   Not exhibiting any symptoms of disease, as for example in a case which is subclinical (“without signs detectable by physical examination or laboratory test”).

Noun

1. 1
   A person or an animal that exhibits no symptoms of disease.
2. 2
   Preceded by the: people or animals that exhibit no symptoms of disease regarded collectively.