The air sound is quite common in English, but when we consider all the thousands of words in the dictionary, it occurs in surprisingly few words. Only about thirty commonly used words use the are spelling, including bare. care. dare. Only about a dozen words have the air spelling: hair. pair. repair. And fewer than half a dozen have the ear spelling, as in bear. pear. swear. and one of these (tear) has two sounds and two meanings.
Prayer is the word pray with the suffix -er. Over the years the pronunciation has shortened the sound to prair.
We also have words that have the sound but don’t contain the letter A. These include there, their, they’re, where and wer. Another is heir with a silent H. The first five words are of Germanic origin, but heir is a French word of Latin origin.
As for the word air, does anybody, anywhere, still call an airport an aerodrome? Some very old stubborn Brits still call airplanes aeroplanes, but it is interesting to note that we also have not fully switched the spelling. We call stunts with airplanes aerobatics and we write about aerial photography. Also that thing we call an antenna and poke up into the air is still sometimes called an aerial. So we can see that aer and air are still in transition.
Meanwhile, there are also plenty of companies that use the word aero, including the producers of that popular delight Aero Chocolate Bars. These are sold in 40 different countries, including Canada….but are not available in the United States. Pity.