While the modern English word doom refers to unavoidable, dreadful calamity, its original sense is simply ‘that which is put down’, deriving from the Proto-Indo-European root *dʰeh₁- ‘to do; to put, place’. Indeed, it is a direct cognate of Ancient Greek θωμός ‘heap’. In the Germanic branch it has acquired the meaning ‘judgement, verdict’, whence the English doom, deriving from the Christian Doomsday, literally ‘Day of Judgment’.
This etymology is well known. In fact, I got it from Wiktionary. What is less well known, however, is the specialized meaning the term carries in old Germanic poetry, namely that of ‘fame, glory’.
The best known example is in the 77th verse of the C9th Speeches of the High One (Old Norse: Hávamǫ́l), which may be the single most well known verse of Old Norse poetry—perhaps behind Egill’s third loose verse, courtesy of the Vikings on the History channel. In my normalization and translation:
Dęyr fé, · dęyja frę́ndr,
dęyr sjalfr hit sama;
ek vęit ęinn · at aldrigi dęyr:
dómr of dauðan hvęrn.“Cattle die; kinsmen die; oneself dies the same.
I know one that never dies: the doom o’er each man dead.”
It would be easy to simply translate dómr here as ‘judgement’ or ‘verdict’ and leave it at that, interpreting it as “how posterity will judge your actions, good or bad”. This has the support of the Norse poetic corpus; in the new Lexicon Poeticum1, documenting words in Scoldic poetry this word is never translated as ‘glory’.
I see two arguments against this interpretation. The first is consistency with the previous verse (76), which shares the first two lines (dęyr … sama) with 77 above, but has its own following two lines:
en orðstírr · dęyr aldrigi
hvęim’s sér góðan getr.“but a word-glory never dies, for whomever gets himself a good one.”
The important word here is orðs-tírr ‘word-glory’ (Old Norse orð has a somewhat broader sense than its English cognate word, and can also mean ‘speech, uttering’). If we consider the parallelism between the two verses, we would expect dómr to mean roughly the same thing.
Secondly, although this meaning is not present in the Norse poetic corpus (which, it should be said, is almost all of a younger date than the Hávamǫ́l), it is in the Anglo-Saxon. Thus, in Beewolf, ll. 1384–1389, where the eponymous hero consols king Rothgar after Grendle’s mother has slain his trusted advisor Asher (Ęschere):
Ne sorga, snotor guma! · Sélre bið ę́ghwę́m,
þęt hé his fréond wrece, · þonne hé fela murne.
Úre ę́ghwylc sceal · ende gebídan
worolde lífes; · wyrce sé þe móte
dómes ę́r déaþe; · þęt bið drihtguman
unlifgendum · ęfter sélest.“Sorrow not, wise man! ’Tis better for each one, that he avenge his friend than that he mourn much. Each one of us shall suffer the end of worldly life—win he who might doom before death: that is for the warrior, unliving, afterwards the best.”
Here the word dóm undoubtedly means glory. It occurs in a number of other places in the poem, for instance in reference to the famous hero Syemund (Sigemund; Old Norse Sigmund), ll. 884b–887a:
[…] Sigemunde gesprong
ęfter déaðdęge · dóm unlýtel
syþðan wíges heard · wyrm ácwealde
hordes hyrde […]“For Syemund sprang up after his death-day an unlittle [great] doom, since hard of conflict he defeated the Worm, the herder of the hoard.”
or in ll. 953b–955a, part of Rothgar’s congratulatory speech to Beewolf after he slays Grendle:
[…] þú þé self hafast
dę́dum gefremed · þęt þín dóm lyfað
áwa tó aldre […]“Thou hast for thyself by deeds accomplished that thy doom [will] live for ever and ever.”
These examples are not exhaustive, but the meaning of the word is clear. The parallels to Hávamǫ́l 76–7 are striking in other ways as well. Thus in 955a the good doom Beewolf has earned, it is said, will live áwa to aldre ‘for ever and ever’, literally ‘forever in the age’. Here the last word is the same as Old Norse aldri-gi ‘never’, literally ‘not in an age’ used in both 76 and 77. Also notable is the shared association of the word with death, seen above in Beewolf 885b (ęfter déaðdęge ‘after death-day’) and 1388a (ę́r déaþe ‘before death’).
What I think we are looking at, then, is a specialized, archaic, meaning of the word doom. As for how this developed, it may very well be the verdict of one’s deeds, but by the time of these sources it is not a neutral term, rather a positively loaded one. The collocation together with die, death is natural, as the two roots both alliterate on d-, and allow the poets to reflect on death and what lives on after it.
Lastly, I see no reason that this collocation not be reconstructed in Proto-Germanic, considering that it is attested in two separate Germanic branches. (Indeed, the idea of immortal fame goes back all the way to the Proto-Indo-Europeans!2) The relevant forms may be reconstructed as *dōmaz, *dawjaną, and *dauþuz.
https://lexiconpoeticum.org/m.php?p=lemma&i=14161
I am of course speaking of the well known Græco-Aryan formula going back to *ḱléwos n̥dʰgʷʰitóm, which has been elaborated on in detail by C. Watkins (1995) in How to Kill a Dragon, Oxford University Press.