In Modern Standard Arabic, phonemic /lˤ/ (a.k.a. "emphatic l") only occurs in one native word: Allah /ʔalˤˈlˤaːh/. (According to the linked article, it also occurs in a few loanwords.)
This seems like a profoundly weird situation. If a phoneme exists at all, you'd expect it to show up more than once. Imagine a time before the loanwords with /lˤ/ were borrowed. Would allah then have been the only instance of /lˤ/ in the entire lexicon of the language? I know that's logically possible, but intuitively it strikes me as completely bizarre.
So what happened? How did this weird situation come about? (Or is it less of a weird situation than I think? I'd be happy to hear about other languages that have similar "one-off" phonemes.)