Yes. In Jain Dharma, every Tirthankar is an Arihant, because a Tirthankar has destroyed the ghati karmas and attained kevalgnan.

But not every Arihant is a Tirthankar. A Tirthankar is a special Arihant who establishes the tirtha—the Jain sangh of monks, nuns, shravaks, and shravikas.

So the correct understanding is:

• Tirthankar = Arihant
• Arihant ≠ always Tirthankar