'basal' originates from New Latin, specifically from the Late Latin adjective 'basalis,' which in turn comes from Latin 'basis' (borrowed from Greek 'basis'), where the Greek 'basis' meant 'a step' or 'a base'.

'basis' in Greek produced Late Latin 'basis' and Late Latin 'basalis', which entered English as 'basal' in the 19th century; the adverb 'basally' developed from the adjective 'basal' by regular English adverbial suffixation ('-ly').

Initially, the root referred to a 'step' or 'base'; over time this evolved into meanings related to the 'base' or 'bottom' of something and then into adjectival and adverbial senses meaning 'at the base' or 'fundamentally'.