Entry 1 sense Webster, 1913 Whitsun /wĭtʹsən/ · Whit·sun · IPA /ˈwɪt.sən/ 01 a. Of, pertaining to, or observed at, Whitsuntide; as, Whitsun week; Whitsun Tuesday; Whitsun pastorals. 1. Of, pertaining to, or observed at, Whitsuntide; as, Whitsun week; Whitsun Tuesday; Whitsun pastorals.