'arsis' originates from Greek, specifically the word 'ἀρσις' (arsis), where the root related to the verb 'αἴρω' (airo) meant 'to lift' or 'raise'.

'arsis' passed into Late Latin and Medieval Latin as 'arsis' and was borrowed into English (from Latin/Greek scholarly usage) with its technical meanings in prosody and music.

Initially it meant 'a lifting' or 'the act of raising' (in Greek physical sense), and over time it came to denote the 'raised/upbeat' portion in metrical and musical contexts.