[ CNRTL : ] Du lat[in] vulg[aire] *hinc ha (c) hora ou *hinc ad horam;
la forme a[ncienne] fr[ançaise] uncore, oncore est due à l'infl[uence] de onque, onc*.
This thread redirects you to the elongations of the the abbreviations used above.
[ Etymonline : ] [...] French encore "[3.] still, [4.] yet, [5.] again, [6.] also, [7.] furthermore" (12c.), generally explained as being from Vulgar Latin phrase
[1.] *hinc ad horam "from then to this hour," or
[2.] (in) hanc horam "(to) this hour" [...]
I can conceive how 1 and 2 shifted semantically to mean 3. For example, a Roman may complain about how a problem has not been resolved from then (when the problem started) to this hour: i.e. how it has STILL not been resolved.
But what underlying semantic notions connect 1-2 to 3-7?