'occidentalis' originates from Latin, specifically from the participial stem 'occidens' (from the verb 'occidere'), where 'occidere' meant 'to fall' (used of the sun) and 'occidens' meant 'west' or 'setting (of the sun)'.

'occidentalis' in Latin developed from 'occidens' (the present participle of 'occidere'). Through Medieval/Scientific Latin the form 'occidentalis' was used as an adjective meaning 'western'; Old French and Middle English yielded the related adjective 'occidental' in modern English, while the full Latin form 'occidentalis' has been preserved in scientific names and formal Latin usage.

Initially it carried the sense 'setting (of the sun)' or 'west'; over time the meaning generalized to 'western' and is now used both as an adjective in learned contexts and as a Latin species epithet meaning 'western'.