The word "flying blister" is spelled using the IPA phonetic transcription as ˈflaɪɪŋ ˈblɪstə. The first part, "flaɪɪŋ," is pronounced with a long "i" sound followed by the "ng" consonant blend. The second part, "blɪstə," has a short "i" sound and ends with the unstressed schwa vowel. This unique spelling reflects the word's origin, likely referring to a blister on the skin caused by friction or burning, that appears to be "flying" through the air.
A vesicating agent applied in succession to different areas of the skin, being kept in each place only long enough to redden, but not to cause a blister.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.
The term "flying blister" is not a commonly used term in English. It is possible that it is a specific term used in a particular context or field, but without further information, it is difficult to determine its exact etymology.