adjective
1.
capable of causing infection
viruses and other infectious agents
Synonyms: infective
Related Word: mephitic, miasmic, noxious, pestilent, pestilential, poisonous, toxic, virulent
Contrasted words: healthful, hygienic, salutary, wholesome
2.
transmissible by infection
infectious diseases
Synonyms: catching, communicable, contagious
3.
easily communicated or diffused
her enthusiasm was infectious
Synonyms: catching, contagious, taking
Related Word: irresistible, sympathetic