Recently, I learned that there is at least one Spanish word that can be pronounced but not written.
It is the imperative form of 'salirle'. It is prononunced as 'sal-le' and the written form should be 'salle'. But according to pronunciation rules, that word must be pronounced as 'sá-lle'. So the word can't be written at all (more details here).
Are there other words that can't be written? Has this phenomena a name?