I don’t wanna make an account for that either lol and I don’t have a physical copy of Macquarie either. The newest Macquarie dictionary I could find on the internet archive that actually had the word Retro in it was the 1989 pocket dictionary. According to that edition, Retro is “a prefix meaning ‘backwards’ in space or time, as retrogression, restrospect.”, but of course that definition is probably outdated.

There’s a 1995 school version, but it doesn’t have the word in it. I looked on the website for my local regions network of libraries, and there’s a 2008 one in my local library two minutes walk away and a 2013 one in a library 20 mins drive away. So you know what, I might just walk down to the library tomorrow and see what it says and let you know haha (nobody here spoil it in the meantime 😄)