Prefix or adjective meaning \"one and a half\"

Prefix or adjective meaning \"one and a half\" References Is there a prefix or adjective that means \"one and a half\", as \"tri-\" or \"triple\" is for \"three\"? The exact usage I have is to describe \"18\" in terms of a dozen. Where I live they\'ve started making 18-egg cartons, and the local grocer was wondering what name to give them in his computerised cash register, hoping for a single word. Even slang, informal or invented term would do if there isn\'t such a term already.