'untagged' is formed in English by adding the prefix 'un-' (Old English 'un-') to the verb 'tag' (Middle English 'tagge', meaning 'label' or 'small piece of cloth used as a label').

'untagged' developed as the past-participle/adjectival form of the verb 'untag', which itself comes from the negating prefix 'un-' + 'tag' (Middle English 'tagge'); over time this produced the modern adjective and past participle 'untagged'.

Initially it literally meant 'not having a tag' or 'tag removed'; this basic meaning has been retained, though use has expanded to digital contexts (e.g., removing social-media tags).