The spelling of the adjective "fleetliest" is determined by the phonemes /ˈflitliɪst/ in American English. The word indicates a superlative degree of "fleet," referring to something that is the most agile or nimble. The first syllable is pronounced with a long "e" sound, while the second syllable features a short "i" sound followed by a schwa. The word's ending is formed with -liest, a common suffix used to modify adjectives to indicate a high level of comparison.
The word "fleetliest" is derived from the word "fleet", which originated from the Old English "fleotan". "Fleet" has its roots in Germanic languages, specifically Old High German "fliozzan" and Old Norse "fliota". The base meaning of "fleet" is to move swiftly or flow, often referring to water. Hence, "fleetliest" is the superlative form of "fleet", meaning the most swift or nimble.