確か

Etymology
From. First attested in the  of 720.

Derived from the tashi- element seen in and  + adjective-forming suffix.

Adjective

 * 1)  certain, clear, without a doubt
 * 2)  secure, reliable, able to be trusted completely

Adverb

 * 1) if I remember correctly, in my memory, probably but not totally sure

Usage notes
Adverbial use without the particle is colloquial. The meaning for this usage implies a degree of doubt, and is different from the, sense of 確か that has no such implication.