The double 'i' is cool, but what's the rule?
At least to a self-professed geek, it's cool to write words like fungii and radii, so naturally, in some informal communications, I take every opportunity to apply the suffix where it's probably not supposed to be used.
Thus I ask, what is (are) the rule(s) for the double 'i'?
The ‘i’ is a Latin plural. ‘Fungus’ is the singular and ‘fungi’ (not 'fungii’) is the plural. The letter ‘i’ occurs twice at the end of ‘radii’ only because there’s an ‘i’ in the singular ‘radius’.