under, beneath: the lower position relative to something above
TranslatabilityDirectCertaintySettled
At its root this word names the under part, the space or position below something. From there it covers everything a person can be under: under a tree, under the heavens, under someone's foot or hand. The same picture of being lower than another carries the sense of being under authority or control, since the one above holds power over the one beneath.
A closely related use keeps the idea of place but drops the up-down picture: to stay put, to remain right where one is, on the spot. Here the word marks the very place a person or thing occupies rather than what is over it. These uses all share one core idea, the position a thing holds, and they shade naturally into the substitution sense in the next meaning, since the thing that takes your place stands where you stood.
in place of, instead of, in exchange for: one thing standing where another would be
TranslatabilityDirectCertaintySettled
When something takes the position another thing held, this word marks the swap. It is the language of substitution: a ram offered instead of a son, one child given in place of one who died, a payment that stands in for a loss. The thing named after the word is what comes in, and the thing it replaces is what goes out.
The same idea drives two common patterns. One is exact recompense, the balanced exchange of life for life, eye for eye, where each side answers the other one for one. The other is succession to office: when a king dies and his son reigns in his place, the heir steps into the spot the father held. All of these keep the single thread of one thing standing in for another, which is what separates this meaning from the plain spatial under.
because, in return for the fact that: a reason given as the price of an action
TranslatabilityDirectCertaintySettled
Joined to a short linking word, this term turns into a reason marker meaning because or in return for the fact that. It grows directly out of the exchange idea: a consequence comes in return for what was done, the reward or punishment standing in place of the deed. So the word keeps its sense of one thing answering another, now applied to cause and result rather than to objects.
In this use it usually points to a deed that earns its outcome, often a wrong that brings judgment or, less often, a faithfulness that brings reward. The reason it gives is weighted as something deserved, an outcome paid out for what came before.
the single Hebrew word covers both succession and plain spatial under, where the English phrase is fixed to replacementGen 18:8
Both
both mark one person stepping into the position another held1Ki 11:43
Only in his stead
in his stead is an old, narrow English phrase used almost only for one person succeeding another in office
“in place of”
Comparison data is not available for this English gloss yet.
“for”
Comparison data is not available for this English gloss yet.
“because”
Comparison data is not available for this English gloss yet.
How taḥat differs from similar Hebrew words
יַעַןa pure because word that gives a reason without any idea of exchange or recompense; this word carries the extra sense of a result paid out in return for a deed.
בְּעַדfor, on behalf of, or around and behind; it covers acting for someone's benefit, while this word marks one thing standing in the place of another.
It sets two things in relation, so the thing above has to be named alongside the thing below it.Gen 1:7Gen 18:4Exo 17:12
It moves from place to substitution, one thing standing in the position of another, so it is often rendered "instead of".Gen 22:13Gen 4:25Gen 44:33
It carries the matching formula of Israel's law, where each loss is answered by its exact counterpart.Exo 21:23Exo 21:24
It can describe being under someone's power or care rather than physically lower than them.Gen 16:9Gen 41:35
It can point to the very spot a person or thing already occupies, which is how a command to stay put says "stay where you are".Exo 16:29Gen 2:21
Both
Both put something low in space, beneath whatever is over it, and English renders them with the same small family of words ("under", "beneath", "lower").Gen 7:19Ezk 43:14
Both belong to the measuring language used for buildings and their furnishings, naming which part sits at the bottom.Exo 25:351Ki 6:6
It is a describing word attached to the thing itself, so it can label something as the low one without naming anything above it.Isa 22:9Ezk 40:18Ezk 40:19
It picks out one level in a stack of levels, the bottom one named beside a middle and a top.1Ki 6:6Ezk 41:7Ezk 42:5Ezk 42:6
It hardens into part of a place name, the town of Lower Beth-horon as against Upper Beth-horon.Jos 16:31Ch 7:242Ch 8:51Ki 9:17
taḥat in the other biblical languages
ὑπόGreek“by/under: by”the ordinary Greek word for under and beneath, and for being under someone's authority; it matches the spatial side of this word but not its instead of sense.
ἀντίGreek“for”the Greek word for instead of, in place of, and in return for; it matches the substitution and exchange side of this word but not its plain spatial under.
What scholars say about taḥat
The standard lexica treat תחת as a substantive meaning the under part that functions as a preposition and, with a linking word, as a conjunction. BDB and HALOT lay out the range as (1) the spatial under or beneath, including being under authority or remaining in one's place, (2) in place of, instead of, in exchange for, covering substitution, the eye-for-eye recompense formula, and succession to office, and (3) the conjunction because or in return for the fact that, normally with asher or ki. The exchange and substitution sense is widely understood to be the bridge from the spatial sense to the causal conjunction.
Sources
Brown, Driver, and Briggs, A Hebrew and English Lexicon of the Old Testament, s.v. תַּחַתlexicon
Koehler and Baumgartner, The Hebrew and Aramaic Lexicon of the Old Testament, s.v. תַּחַתlexicon
Clines, ed., The Dictionary of Classical Hebrew, s.v. תַּחַתlexicon