Entry 3 senses · 2 variants Webster, 1913 ironside /ī'-ẽrn-sīdˌ/ · i·ron·side · IPA /ˈaɪərnsˌaɪd/ n. prop. n. 01 n. a man of great strength and endurance, especially on who is brave. 1. a man of great strength and endurance, especially on who is brave. 02 prop. n. A nickname for Oliver Cromwell. 1. A nickname for Oliver Cromwell. 2. A nickname for Edmund II of England.