Entry 2 senses · 2 variants Webster, 1913 Additional /əd-ĭsh'-ən-əl/ · Ad·di·tion·al · IPA /əˈdɪʃənəl/ a. n. 01 a. Added; supplemental; in the way of an addition. 1. Added; supplemental; in the way of an addition. 02 n. Something added. 1. Something added.[R.]