Webster's Revised Unabridged Dictionary · 1913

Unprobably

Unprobably , adverb

[Prefix un- not + probably.]

Improbably.

Unprobably , adverb

[Un- + Latin probabilis approvable, from probare to approve. Compare Probable.]

In a manner not to be approved of; improperly. [Obsolete & Rare]
To diminish, by the authority of wise and knowing men, things unjustly and unprobably crept in. — Strype