HTML tags are not supported in axis labels. As addressed in previous reply, if you like to break word into multiple lines you can use labelMaxWidth. If you like to add symbols in labels, you can use unicode characters. Please take a look at this thread for more information.
If this doesn’t fulfill your requirements, kindly brief us more about your requirements so that we can understand it better & try to help you achieve the same.
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Vishwas R
Team CanvasJS