Top onion is a term that generally describes the outermost layer of an onion. However, there are several synonyms for this term that can also be used to refer to this part of the onion. Some alternative terms for top onion include onion skin, onion layer, onion shell, onion peel, onion husk, and onion covering. These various synonyms can be used interchangeably to describe the thin, papery outer layer of the onion that protects the layers inside. Whether you prefer to use top onion, onion skin, or any other synonym, these terms all refer to the same part of the onion and are useful for describing its various layers and components.