This seems to be a popular etymology in feminist circles these days.  Hag derives from the Greek hagia for holy.  That is, a holy woman, a mystic, a bridge between heaven and earth.  Just do a google search on [hag hagia] Like this “But [the hag] Cerridwen’s origins are pre-Celtic and the word “hag” is a derivative term of the Greek hagia which meant sacred or sanctuary. “

Interesting that the etymology that I would have confidence in is close, alas, no cigars.

etymonline has: shortening of the Old English hægtesse which may have cognates in the German Hexe and Dutch Heks for witch or fury.  But then also a connection with hedge which may be a border between civilization and the wild world beyond (etymonline).

So this nice lady named Faith at theolog “What a great picture of this woman as a hag—from the word hagia, holy.”

I doubt it.  But the bridge between the meanings is pretty tempting.  Still, folk etymology to be sure.

The writer of your first link has certainly got confused. Cerridwen’s origins may well be pre-Celtic, but what should that have to do with the etymology of the English word ‘hag’?

Perhaps the suggestion is that English ‘hag’ and Greek ‘hagia’ are cognate (which makes more sense than deriving ‘hag’ < ‘hagia’). Now that is quite possible, but with the evidence at hand, there is no etymological support - OED says of the postulated PGmc source that “the ulterior etymology of OTeut. [=PGmc] *hagatusjo:n- is itself unknown.”

Perhaps the suggestion is that English ‘hag’ and Greek ‘hagia’ are cognate (which makes more sense than deriving ‘hag’ < ‘hagia’).

Afraid not.  Neither of them makes a lick of sense, but the latter is at least theoretically possible (if you ignore the fact that hag originally meant “An evil spirit, dæmon, or infernal being, in female form: applied in early use to the Furies, Harpies, etc. of Græco-Latin mythology; also to malicious female sprites or ‘fairies’ of Teutonic mythology” and thus had nothing to do with holiness, and that knowledge of Greek was pretty much nonexistent in 13th-century England); the words’ being cognate is ruled out by the fact that Greek h- (from PIE *s-, *y-) does not correspond to Germanic h- (from PIE *k-) and Greek g does not correspond to Germanic g (PIE voiced stops were devoiced in Germanic, so Greek genos corresponds to English kin).

This is folk etymology at its silliest (and thus most enjoyable).

The Etymologisch Woordenboek van het Nederlands (EWN) has a long article under ‘heks’.
This word too was subject of folk etymology. An older form is ‘hagetisse’ which was homonymous with the word for ‘newt’ (modern Dutch ‘hagedis’, cf. NHG ‘Eidechse’). The newt was also often associated with witchcraft and such. EWN states that the etymology of both words is unclear but continues with some interesting speculations (with many “probablys” and “perhapses”).

It traces the word back to a PGM *haga-tusjo. The second part is probably related to new Nor. tysja ‘elf’, new Dan. tøs, new Swe. tös ‘girl’. According to EWN, the suggested connection with PIE *dhuos ‘spirit’ can not be maintained.
Others suggest a connection with ‘hate’, starting from an older form * haga-hatusi.

The first part, PGM *haga is traditionally identified with PGM haga(na) ‘hedge, fence’.  This would suggest an earlier meaning of ‘wood sorceress’ (with an older secondary meaning of haga ‘wood, forest’ or ‘hiding sorceress’ (from ‘fence’ > ‘shield, hide’). A semantically more likely theory is proposed by Polomé who proposes a connection with OHG hegidruosa, hegidruosi, MLG hagedrose, MDu haechdroese all meaning ‘genitals’. NE ‘hatch’ would be related. Sex, magic and witches are things that, in particular in folklore, were easily combined.

There is also an article in the on-line WNT that even links to the on-line EWN. Unfortunately I can’t get through right now. Besides, the link would only work for those who are registered at WNT (not to mention it is all in Dutch of course).

languagehat: I see the etymology police are on to me for egregious violations of Grimm’s Law. It’s fair cop: what I wrote clearly is, on sober reflection, a crock. I blame society.