'arboreous' originates from Latin, specifically the Late Latin word 'arboreus', where 'arbor' meant 'tree'.

'arboreus' passed into Late Latin and Medieval Latin forms and was adopted into English as 'arboreous', retaining the sense of 'tree-like' or 'of trees'.

Initially, it meant 'of or pertaining to trees', and over time this meaning has remained largely consistent, referring both to tree-related characteristics and to being covered with trees.