Entry 1 sense Webster, 1913 Mastoiditis /măsˌ-toid-īt'-əs/ · Mas·toid·i·tis · IPA /mˌæstɔɪdˈaɪtəs/ 01 n. Inflammation in the mastoid process of the temporal bone. 1. Inflammation in the mastoid process of the temporal bone.(Med.)