The spelling of the word "most desexed" follows English phonetics. The IPA phonetic transcription of the word is /məʊst dɪˈseksd/. The word "most" is pronounced with a long "o" sound and a soft "t" at the end. The word "desexed" is pronounced with a short "e" sound as in "dress" and a hard "x" sound. The word means neutered or spayed, and is commonly used to refer to cats and dogs. Overall, the spelling of this word reflects English pronunciation rules.
The word "most desexed" does not have a specific etymology because it is not a commonly used or recognized term in the English language. "Desexed" usually refers to a state of being sterilized or neutered, often in reference to animals. However, adding "most" before "desexed" seems to create an unusual construction or oxymoron, as "most" implies a superlative degree while "desexed" refers to a binary condition (to be or not to be neutered). Therefore, it is unlikely to have a well-established origin or etymology.