Webster’s 1913 has no entry under this spelling.
Shades of meaning
Fernald has no entry of its own for in the midst of; he lists it under amid.
Where he writes about it:
In the midst of may have merely the local meaning; as, I found myself in the midst of a crowd; or it may express even closer association than among; as, "I found myself in the midst of friends" suggests their pressing up on every side, oneself the central object; so, "where two or three are met together in my name, there am I in the midst of them," Matt. xviii, 20; in which case it would be feebler to say "among them," impossible to say "amid them," not so well to say "amidst them." — from amid