I am wondering whether there are out there online English dictionaries which group words with identical roots together to simplify learning.
For example when I learn verb "subdue" it would be great to know immediately that the related noun is "subdual", and probably there is an adjective which I do not know yet.
Cambridge Dictionary does list related words together (e.g. in the case of sardonic it also let me know about sardonically) but not in all cases (e.g. in the case of purpose no mention of purposive can be found).