Entry 3 senses · 2 variants Webster, 1913 Adventive · Ad·ven·tive · IPA /ədˈvɛntɪv/ a. n. 01 a. Accidental. 1. Accidental. 2. Adventitious.(Bot.) 02 n. A thing or person coming from without; an immigrant. 1. A thing or person coming from without; an immigrant.[R.]