Entry 2 senses · 2 variants Webster, 1913 Noonday · Noon·day · IPA /ˈnundeɪ/ n. a. 01 n. Midday; twelve o'clock in the day; noon. 1. Midday; twelve o'clock in the day; noon. 02 a. Of or pertaining to midday; meridional; as, the noonday heat; only mad dogs and Englishmen go out in the noonday sun. 1. Of or pertaining to midday; meridional; as, the noonday heat; only mad dogs and Englishmen go out in the noonday sun.