actinomycosis ak ti noh mahy koh sis n disease of cattle that can be transmitted to humans; results from infection with actinomycetes; characterized by hard swellings that exude pus through long sinuses Usage(s) Diseases against which penicillin is effective but not fully tested: syphilis, actinomycosis, bacterial endocarditis. Diseases against which penicillin is effective but not fully tested: syphilis, actinomycosis, bacterial endocarditis.