An airsmith is a gunsmith that services, repairs or modifies airguns rather than firearms. The term is most commonly applied to those who work on paintball guns (often called markers) but can also apply to those who service pellet guns.
The term "airsmith" may also apply to those who work on Airsoft guns. It, more generally, applies to those who specialize in servicing high-pressure air systems, which can prove extremely hazardous if not professionally maintained or installed. Even mundane fittings can turn into dangerous missiles at extreme pressures, so it is important to ensure anything involving high pressure gas is professionally installed.