'aro' originates from English, specifically as a clipped/informal form of 'aromantic' (itself formed from the prefix 'a-' meaning 'not' plus 'romantic').

'aromantic' emerged in late 20th/early 21st-century LGBTQ+ discourse to describe lack of romantic attraction; 'aro' developed later as a shortened, community and internet-used label for 'aromantic' and came into wider use in the 2010s.

Initially 'aro' was simply shorthand for 'aromantic'; over time it has become a widely used identity label and an adjective as well as a noun within and beyond LGBTQ+ communities.