I like Gibby, it's like an English public school nickname. Gibby and his sister Bunty.
I'm a big fan of
Gabriel "
Gabby", so why not
Gabriel "Gibby"? And, of course,
Gilbert would be a darling full name for Gibby.
Agape "Gibby", for a girl?
Ottilie
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http://www.behindthename.com/pnl/116467