Since the word doesn't occur in the OT, it's hard to know for sure. I found צְלָב, which makes sense given that the Syriac (and presumably other Aramaic forms) is ṣleeba. It's Modern Hebrew, but the word is unlikely to be different; Modern Hebrew generally differs more in grammar than spelling. Checking rabbinic works would be the only way to be sure, but most of that is Aramaic anyway. I have an exceptionally knowledgeable Israeli friend I can ask.
