This tag should be used for questions about choosing the right words for the context of your writing. Questions about etymology and grammar are off-topic.
The tag word-choice is for questions that deal with the words and vocabulary that should be used when writing different kinds of texts. This can include finding the right voice for your narration or for your technical document, for example. In these cases it could be combined with the tag voice. It can also be appropriate for questions about phrasing information so that it is easily understood, or for questions about convincing dialogue in a historical setting.
The tag is not intended for questions about etymology or grammar. These may generally be more on-topic on the various language sites of Stack Exchange, such as the English Language & Usage site.