'cactoid' originates from Neo-Latin/modern formation, specifically the stem 'cact-' ultimately from Greek 'kaktos' meaning 'spiny plant' (via Latin 'cactus'), combined with the suffix '-oid' from Greek 'eidos' meaning 'form' or 'likeness'.

'cactoid' was formed in modern English by combining the element 'cact-' (from Latin 'cactus', from Greek 'kaktos') with the Greek-derived suffix '-oid' (from 'eidos' via Latin/modern combining forms), producing the adjective/noun meaning 'cactus-like'.

Initially it meant 'like a cactus' (i.e., resembling a cactus in form); over time the usage has remained broadly the same, used both descriptively for form and technically in botanical contexts.