The U2414H comes with a MiniDisplayPort-DisplayPort cable. This allows you to connect a monitor via Thunderbolt. That's what I do here with my MacBook Pro. However, I have two Thunderbolt ports and connect the second monitor in the same way.
For you, DaisyChaining might be an option. However, I don't know if this works with Mac. The best thing to do is to google MacBook Air Daisy Chaining or similar.