ɪˈɹʌpʃən ˈaʊtbɹeɪk the emergence of a tooth as it breaks through the gum a sudden very loud noise a sudden violent spontaneous occurrence (usually of some undesirable condition) the outbreak of hostilities the sudden occurrence of a violent discharge of steam and volcanic material (of volcanoes) pouring out fumes or lava (or a deposit so formed) symptom consisting of a breaking out and becoming visible