Creating a crossword activity in your Moodle course for practicing concepts, can be achieved from various ways like through the Game activity module. But the problem is that all of them came up with a lot of other code which can’t be removed while keeping only crossword activity.
Itamar Tzadok has shared a dataform field that generates and displays a crossword in Moodle forums. The Dataform crossword uses open code by Àngel Fenoy from Arenys de Mar, Barcelona for generating the crossword structure (the same code that is used by the game plugin). It uses open js code and jquery for the crossword ui.
The dataform crossword field plugin can be downloaded from github here. It requires Dataform 2.8.6.
Reference forum thread: https://moodle.org/mod/forum/discuss.php?d=314017#p1263971