'astral' originates from Latin, specifically the word 'astralis', where the root 'astr-' ultimately comes from Greek 'astron' meaning 'star'.

'astral' changed from Latin 'astralis' (and via Medieval/Modern Latin and Old French usage) and eventually became the modern English word 'astral'; the adverb 'astrally' was formed from that adjective.

Initially it meant 'pertaining to the stars', but over time it also acquired the related sense of 'pertaining to the astral (occult/spiritual) plane', which is reflected in modern usage.