Entry 1 sense Webster, 1913 Haecceity /(hĕk*sē"ĭ*ty̆)/ · Haec·ce·i·ty · IPA /hɛkˈsiː.ə.tiː/ 01 Literally, this-ness. A scholastic term to express individuality or singleness; as, this book. 1. Literally, this-ness. A scholastic term to express individuality or singleness; as, this book.(Logic)