basal / basil are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
basal: (adjective) serving as or forming a base. (adjective) of primary importance.
basil: (noun) any of several Old World tropical aromatic annual or perennial herbs of the genus Ocimum. (noun) (Roman Catholic Church) the bishop of Caesarea who defended the Roman Catholic Church against the heresies of the 4th century; a saint and Doctor of the Church (329-379). (noun) leaves of the common basil; used fresh or dried.
basal: b·EY·s·ah·l
basil: b·AE·z·ah·l
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)