List of diminutives ending with -o
They're formed by shortening a longer word and adding an o (in contrast with condo, Lambo, psycho where the o pronunciation is part of the original word; or with lingo which is Latin lingua + o.)
I wonder, for some of them, just how broadly they would be understood.
Australian English is said to be pretty productive with this. My impression is that a word such as convo would be easily understood by Ozzies, but not necessarily by, say, Americans.