Google says it means "you" and is pronounced "mí"
Wiktionary says it is "you" but only for deity and pronounced “nǐ”
My pinyin input method offers it for "mi" or "ni"
CEDICT makes it a "memorial tablet in a temple commemorating a deceased father"（or a surname) and pronounced "mǐ"
I'm guessing all three meanings are correct, but that would mean at least one of the pronunciations is wrong (since Google and Wiktionary give it the same meaning with different sounds).