Manatees are giant herbivorous sea cows native to the Caribbean. Therefore, Europeans didn't come into contact with them until the Spanish started exploring the region. There, it is theorized that picked up a local Taino word for the animal, which subsequently became the Spanish word manati, and eventually English manatee. It's likely the indigenous word meant "breast", and was applied due to a shared connection of bulbousness between the two. However, the origin is disputed. Some etymologists trace it to the Latin word manatus, which means "having hands", from the root manus, "hand" (referring to the large flippers manatees have). This, through Proto-Italic, would originate in the Proto-Indo-European reconstruction for "hand", which varies from mehr to mehn to man. Usage of the word manatee has been steadily increasing since its first application in the 1750s, and likewise for Spanish since the 1630s.
Adam Aleksic, a leading contender for valedictorian of his high school, is a 208-month-old boy with disturbing interests in etymology, vexillology, geography, and law. Adam would like to one day visit Tajikistan and just won an essay contest on linguistics!
The Etymology Nerd