“And God said, ‘Let the waters under the heavens be gathered in one [אחד] place so that the dry land will appear’, and so it was.” (Robert Alter)
The vast majority of Hebrew term's classes are derived from conceptual roots. Now, admittedly, one of the most difficult aspect of ‘Biblical’ Hebrew to understand is to fix the correct link between derivatives terms and conceptual roots (“The ascertaining of the root and its meaning, although in many ways very difficult and hazardous, is of great lexicographical importance [...].”, F. H. Wilhelm Gesenius, Hebrew Grammar, § 30i).
In the matter on the discussion, it be quite simple to make to derive אחד from the same conceptual roots of the numeral ‘one’, and maybe, with the term אח (‘brother’, ‘relative’, ‘kinsman’, et cetera). In the same manner, also the allographic root יחד can be related with the same concept (see, please its usage in Gen 49:6).
All these terms have in common an idea of ‘to be cohesive, unified’ (see the idiom למען יהיו כלם אחד – only for a comparison purpose - in John 17:21, The New Testament in Hebrew and English, Cambridge University Press.
So, is it all ok?
Don’t these facts confirm the commoner translation ‘the waters […] be gathered in one [אחד] place’?
Not quite, because the trouble is the context.
From the Genesis’ passages (1:2, 6) we learn that Earth was (in the epoch pointed by these verses) a planet fully covered by the waters. So, also in that time the waters were in one place, don’t they?
Why, so, the supposed 'one place' seems to appear only on the second ‘day’?
Happily, the phraseology of the verse 9 can help us to understand that only after the waters’ setting apart the dry land was able to appear. In the spectacular poetry of Job 38:8-11 we just find the Bible link between waters (sea) and his 'setting apart'. In fact, we read in it (bold is mine):
“Or who shut up the sea with doors, when it broke forth, as if it had issued out of the womb? When I made a cloud its garment, and thick darkness a swaddling band for it, And broke up for it my decreed place, and set bars and doors, And said, Hitherto shalt thou come, but no further: and here shall thy proud waves be stayed” (Webster)”
It shouldn’t be probable, then, that the term אחד, was derived not from a root with a ‘to unify’ (et cetera) concept, but from a root related with the idea of ‘to set apart’, ‘to back‘, to corner’, ‘to close (in a limited space)’, and so on?
A conceptual root that has these necessary requirements exists.
We find it – transformed in a verbal form - in Eze 21:19 (in other numerous passages we find this root transformed in a noun as ‘an enclosed place’):
So, if we conclude that the term אחד in Gen 1:9 was derived from the root חדר, we can discover a fresher and – more importantly – suitable meaning of the verse at issue, without triggering any clash with the logical context of the passage: