More: comes from the Old English mara, same meaning. Mara is what’s known as a comparative. In the same way good is related to better, mara is related to the Old English micel, or great. And believe it or not, micel has a modern form: mickle, a never used word for large (it’s not even in Word’s dictionary).
Less: was laes/laessa in Old English, and like more, was a comparative of laes—small. It comes from the Proto Germanic lais-izo, smaller, and the Proto Indo European leis, small.
Always: showed up in the mid-fourteenth century, although back in Old English it was two words: ealne weg, which literally meant all the way. Fun fact: it used to be just alway. The s appeared in the early thirteenth century, although the non -s form didn’t disappear until just the nineteenth century.
Just: the righteous form of just showed up in the late fourteenth century but the adverb didn’t show up until the mid-sixteenth century. Middle English also used just as a word for exactly or precisely, and Modern English then morphed it to barely.
Often: Showed up in the early fourteenth century as a form of oft that went before vowel sounds, much like a and an. But unlike a and an, often ended up replacing oft almost completely.
Very: these days we mostly use very as emphasis (it’s not just bad, it’s very bad) rather than extremely or high degree like it meant originally. Very showed up in the mid-thirteenth century as verray, which at first meant real or genuine but switched to actual or utter in the late fourteenth century. You might remember that I mentioned very in the truth post a few weeks ago as having descended from the classical Latin verus. To be more specific, verray descends from the Anglo French verrai, the Old French verai, Vulgar Latin veracus, and the classical Latin verax (truthful), which is from verus.
Tony Jebson’s page on the Origins of Old English