> > Hrafn flýgr austan
> af hám meiði,
>
> 'meiðr' is a poetic
> synonym for "tree", see Zoega 'meiðr' (3).

...which can also mean a pole or the runner of a sledge, or (in
poetry) a gallows. I suggested you might have been thinking of 'mein'
"harm", but actually there's a whole bunch of even more similar words:

meiða - to harm
meiðing - bodily hurt, maiming, damaging
mei(ð)zl, meizli, meizlur - injuries, mutilations
meiðir - injurer (in poetry)

I'm a bit puzzled by the statement in Cleasby/vigfússon that "the word
[meiðr] can never be used of a living tree." The Lexicon Poeticum
specifically says that it can be used of a "living tree" (levende træ).

http://www.septentrionalia.org/lex/index2.php?book=d&page=399&ext=html

Besides the formulaic association of 'meiðr' with 'hrafn', it's used
of the world ash Yggdrasill:

á þeim meiði
er manngi veit
hvers af rótum renn
(Hávamál)

hygg ek, at æ skyli
meiðs kvistu má
(Grímnismál)

Mímameiður hann heitir,
en það fáir vita,
af hverjum rótum rennur;
(Fjölsvinnsmál)

meiðs kvistum Míma;
(Fjölsvinnsmál)

...and of the "mistletoe" conceived as a tree in Völuspá:

Varð af þeim meiði,
er mær sýndist,
harmflaug hættleg