* Smallest by mass: The smallest stars in Orion are likely red dwarf stars, which are too faint to be seen with the naked eye. We don't have precise measurements for all the stars in Orion, so it's hard to say definitively which is the smallest by mass.
* Smallest by apparent size: The star that appears smallest in the night sky from Earth is Meissa (Lambda Orionis). It's a blue giant star, but it appears small because it's very far away.
Therefore, depending on what you mean by "smallest", there's no one definitive answer.
