Actinomycosis \Ac`ti*no*my*co"sis\ ([a^]k`t[i^]*n[-o]*m[imac]*k[=o]"s[i^]s), n. [NL.] (Med.) A chronic infectious disease of cattle and man due to infection with actinomycetes, especially by {Actinomyces bovis} in cattle and by {Actinomyces israeli} or {Arachnia propionica} in man. It is characterized by hard swellings usually in the mouth and jaw. In man the disease may also affect the abdomen or thorax. In cattle it is called also {lumpy jaw} or {big jaw}. [Webster 1913 Suppl. + AS]