Prior to Tolkien the adjective was 'elfin' or 'elfish' actually. These are still valid, but now much less used than 'elven' and 'elvish'. And yet, the 'Tolkien' style is the older and original style!
In fact the 3rd edition of the American Heritage Dictionary still lists only 'elfin' and not the newer/older style 'elven'.
elfˇin -- adjective
1. a. Relating to or suggestive of an elf. b. Made, done, or produced by an elf.
2. Small and sprightly; mischievous.
3. Having a magical quality or charm; fairylike: moved across the dimly lit stage with elfin grace.
elfˇish also elvˇish -- adjective
1. Of or relating to elves.
2. Prankish; mischievous.
It's the same with dwarf -- dwarfin/dwarfish and dwarven/dwarvish. Tolkien revived the older style. Somewhere or other in the Letters he sets out the argument why this is in fact the
correct form but I don't know where to find it now. He was a philologist, remember. The dainty 'elfin/dwarfin' form is a pseudo-Medieval coinage from the late Renaissance/Shakespearean times.