The phrase "wast air" is an archaic way of referring to empty or wasted space. There are several synonyms for this phrase that can be used in modern English. The first and most popular synonym is "empty space," which refers to an area without any visible objects. Another synonym is "void," which gives off a sense of emptiness or nothingness. "Vacuum" is also a synonym, referring to a space entirely devoid of matter or air. Additionally, the words "hollow" and "bare" can be used interchangeably with "wast air" to convey the same sense of emptiness and lack of substance.