Mistrust, v. t.
1. To regard with jealousy or suspicion; to suspect; to doubt the integrity of; to distrust. I will never mistrust my wife again. Shak.
2. To forebode as near, or likely to occur; to surmise. By a divine instinct, men's minds mistrust Ensuing dangers. Shak.
1 other Webster entry under this spelling
Mistrust, n.
Want of confidence or trust; suspicion; distrust. Milton.
Shades of meaning
Fernald has no entry of its own for mistrust; he lists it under doubt.
Where he writes about it:
Mistrust and suspect imply that one is almost assured of positive evil; one may distrust himself or others; he suspects others. — from doubt
Mistrust is now rarely, if ever, used of persons, but only of motives, intentions, etc. — from doubt
Distrust is always serious; mistrust is often used playfully. — from doubt