Webster’s 1913 has no entry under this spelling.
Shades of meaning
Fernald has no entry of its own for unavailing; he lists it under vain.
Where he writes about it:
That which is bootless, fruitless, or profitless fails to accomplish any valuable result; that which is abortive, ineffectual, or unavailing fails to accomplish a result that it was, or was supposed to be, adapted to accomplish. — from vain