The action to make something larger by filling it with air is called?

The action of making something larger by filling it with air is specifically referred to as "inflate." The term "inflate" comes from the Latin word "inflata," meaning "to blow up." When you inflate an object, such as a tire or a balloon, you are increasing its volume by introducing air into it under pressure. This process is essential in various applications, such as in transportation (tires), recreational activities (balloons, inflatable toys), and even in specific industrial processes.

The other terms provided do not relate to the act of filling something with air. For instance, "loosen" generally refers to making something less tight or less firmly held, which does not involve the introduction of air. "Leck" is not an English term used in this context and does not convey a meaning related to air or inflation. Lastly, "schmieren," which translates to "to smear" in German, also does not pertain to the action of filling something with air. Therefore, "inflate" is clearly the correct and most applicable term in the context of enlarging an object by introducing air.