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.
Best Answer
Sesqui-.
However, it certainly isn't informal, and is also pretty obscure. About the only use of it is sesquicentennial and sesquipedalian which is at a few removes (it literally means 18inches long but it's originally figurative meaning of using long words is the only English meaning).
It certainly wouldn't go with dozen; one would just say "one and a half dozen", "dozen and a half" or "eighteen".
Edit:
If you really want a word meaning 18 of something, you've got octodecuple, which has been used in mathematics at least as far back as 1816 and probably earlier. But really, don't; unless you're talking about properties of mathematical tuples where octodecuples are interesting in some particular way, it would just be horrible.