Synonyms for Contagious:

adj.

baneful (adjective)
calamitous, ill, poisonous, baneful, cursed, infectious, cancerous, evil.
communicable (adjective)
deadly, Impartible, epizootic, infectious, spreading, transmittable, poisonous, catching, taking, transmissible, pestiferous, epidemic, Inoculable.
dangerous (adjective)
pestilent.
unhealthy (adjective)
poisonous, infected, contaminated, insalubrious, malignant, pestilent, unhealthy, unwholesome, deadly, septic, toxic, unsanitary, gangrenous, unhygienic, noxious, pathological, diseased.
widespread (adjective)
epidemic.

n.

central, abstract, orthodox, metaphysical, conceptual, deterministic, theoretical, utopian, popular, nonconformist. advanced, acute, clinical, benign, asymptomatic, autoimmune, move, taking, congenital, chronic. frail, failing, unfit, worse, unwell, fragile, sick. communicable (noun)
epizootic, Impartible, tending to spread, epidemic, spreading, Inoculable, pestiferous, taking.
contagious (noun)
transmittable, infectious, transmissible, communicable, catching, contractable.

Other synonyms:

taking. Other relevant words:
chronic, theoretical, worse, metaphysical, clinical, transmittable, popular, communicable, benign, fragile, spreading, abstract, utopian, pestiferous, unwell, asymptomatic, nonconformist, advanced, unfit, acute, move, epizootic, taking, frail, orthodox, autoimmune, contractable, Inoculable, failing, Impartible, sick, catching, conceptual, deterministic, central, epidemic, congenital, transmissible.

Usage examples for contagious

  1. There is a contagious disease that kills them off in very great numbers. – The Insect Folk by Margaret Warner Morley
  2. Nothing is so contagious as alarm. – Jack Tier or The Florida Reef by James Fenimore Cooper