The BSB foot note for "Dumah" in Isa 21:11 says this:
Dumah is a wordplay on Edom, meaning silence.
This is confirmed by the following parallel statement in the second half of the verse:
One calls to me from Seir, (another name for Edom)
All interpreters of this brief prophecy agree that it is both brief and obscure. here is what we can say about this brief piece of poetic Hebrew:
- "watchman" is a term used very generally for any person, especially prophets who deliver divine messages, eg, Eze 3:17, 33:2, 7, Hos 9:8, Job 27:18, Ps 127:1, Isa 21:6, 8, 9, etc.
- The clever word-play of turning Edom into "silence" is part of the prophecy - Edom was doomed to silence and obscurity. Indeed, they disappear from history soon after the second century.
Ellicott suggests this:
Probably here, as in Isaiah 21:1 and Isaiah 22:1, we have a mystical
prophetic name, Edom being altered to Dumah, i.e., “silence,” as in
Psalm 94:17; Psalm 115:17, the silence of the grave. In this case, as
in the preceding, there is first the oppressive silence of expectancy,
and then of desolation.
He calleth . . . out of Seir . . .—The subject is indefinite: one
calleth. The watchman hears the silence of the night broken by a voice
from Seir. It is probable that the prophet had actually been consulted
by the Edomites, and that this is his answer to their enquiries. The
cry is, “Watchman, what part of the night?” In the weary night of
calamity the sufferer desires to know what hour it is, how much of the
darkness still remains to be lived through. The answer is mysterious
and ill-boding. There is a “morning” coming, a time of light and hope,
but the day which is so opened closes too quickly in the blackness of
night (Amos 5:18). The words sum up the whole future of Edom, subject
as it was to one conqueror after another, rising now and then, as
under Herod and the Romans, and then sinking to its present