Uncertain means not knowing — either you personally, or nobody at all. Standing on the platform with a ticket in your hand and no idea whether the train is still coming.
It points two ways. A person is uncertain ABOUT something or uncertain OF it: I'm uncertain about the date. A thing is uncertain when nothing has been settled — an uncertain future, an uncertain result, the weather uncertain all week. It also describes a shaky manner: an uncertain voice, uncertain steps on the ice. The noun is uncertainty. One phrase runs against the grain, so watch for it: telling someone something in no uncertain terms is telling them very bluntly indeed.
Uncertain arrived whole from Middle English uncerteyn: certain with un- stuck on the front. English has been building opposites this way for so long that the prefix has gone almost invisible.
Middle English
uncerteyn
English, today
uncertain
From Middle English uncerteyn. by surface analysis, un- + certain.
Etymology from Wiktionary, CC BY-SA