Learn Italian: Credo che Santo Stefano sia un uomo santo. - I believe that Saint Stephen is a holy man.

When used as a title before a male saint's name, santo usually shortens to San before a consonant (like San Pietro). However, because Stefano starts with an 's' followed by another consonant (an 'impure s'), the word Santo does not truncate. It keeps its full form so the consonants don't crash together in speech.

Why didn't the second santo in un uomo santo get shortened?

The word santo only drops its final vowel when it is used as a title placed directly before a proper name. In the second half of the sentence, it is acting as a normal adjective meaning 'holy' and comes after the noun (uomo), so it keeps its regular full form.

Why is the verb sia used here instead of è?

Sia is the subjunctive form of essere (to be). You need to use the subjunctive mood here because the sentence starts with Credo che (I believe that), which introduces a subjective opinion, thought, or belief.

Does the word santo change meaning based on how it is used?

Yes, context is key. When used as a noun or a title before a name, it means 'Saint' (as in Santo Stefano). When used as a descriptive adjective, it translates to 'holy' or 'saintly' (as in un uomo santo).