'arrhizal' originates from New Latin/Modern Latin, ultimately from Greek elements: the prefix 'a-' (from Greek a-, meaning 'not') plus 'rhiza' (Greek 'rhíza', meaning 'root').

'arrhizal' was formed in scientific/technical usage from New Latin 'arrhiza' (or Greek-derived formation) and was adopted into English as the adjective 'arrhizal' in botanical and mycological contexts.

Initially formed to mean 'without roots' in specialized biological descriptions; this core meaning has been retained in modern scientific usage.