All of the provided options can help readers define words in different contexts, but if we are to choose the most relevant one:
etymological patterns – They help readers understand the origins and historical development of words, which can provide valuable context for their meanings.
However, if focusing solely on definitions as found in a dictionary, parts of speech would also be crucial, as they indicate how a word can be used in sentences.
If you need to select only one, etymological patterns is often the most informative in terms of deepening understanding of a word's definition.