You can extend default WordPress search feature to show relevant results even if the query you entered matches a single word in any blog post, this way your WordPress search box will find those posts that contain any of the words entered instead of only posts that contain all of the words searched. It makes WordPress search use OR operator instead of default AND operator
Add tags automatically rather than manually. Using Automatic Post Tagger plugin by Devtard all you have to do is create a list of tags with related words for each of them and this plugin automatically adds relevant tags when a post is published or updated. Also it offers you the feature to import those tags which are already present in your database and assign them to all posts.