'twas /twoz, twəz/ (archaic or dialect) a contraction of it was

• immunizing
• immuno-
• immunoassaies
• immunoassay
• immunoassays
• immunoblot
• immunoblots
• immunochemical
• immunochemically
• immunochemistry
• immunocompetence
• immunocompetent
• immunocompromised
• immunocytochemical
• immunocytochemically
• immunocytochemistry
• immunodeficiency
• immunodiagnostics
• immunoelectrophoresis
• immunoelectrophoretically
• immunofluorescence
• immunogen
• immunogenetics
• immunogenic
• immunogenicities