Dajstill,
From Wikipedia:
The phrase mercy seat is not a translation of the Hebrew term kapporeth, which appears in its place in the Masoretic text, nor of the Greek term hilasterion, which takes the same place in the Septuagint, but instead is the translation by William Tyndale of the German term Gnadenstuhl, from the same narrative position in the Luther Bible; Gnadenstuhl literally means seat of grace, in the sense of location of grace.
Though kapporeth is probably derived from kaphar, which is often considered to mean cover, the literal meaning of kaphar is wipe out, implying that kapporeth means thing of wiping out/thing of cleansing. Similarly hilasterion etymologically means thing for propitiation, with Hesychius writing that a synonym of hilasterion was thing for catharsis, while the Vulgate translates it as propitiatorium.
So it appears that "mercy seat" is not a good translation of H3727.
Here are some translations of 1Ch 28:11:
1Ch 28:11
(Geneva) Then Dauid gaue to Salomon his sonne the paterne of the porch and of the houses thereof, and of the closets thereof, and of the galleries thereof, and of the chambers thereof that are within, and of the house of the mercieseate,
(JPS) Then David gave to Solomon his son the pattern of the porch of the temple, and of the houses thereof, and of the treasuries thereof, and of the upper rooms thereof, and of the inner chambers thereof, and of the place of the ark-cover;
(KJV) Then David gave to Solomon his son the pattern of the porch, and of the houses thereof, and of the treasuries thereof, and of the upper chambers thereof, and of the inner parlours thereof, and of the place of the mercy seat,
(The Scriptures 1998+) And Dawiḏ gave his son Shelomoh the plans for the porch, and its houses, and its treasuries, and its upper rooms, and its inner rooms, and the place of atonement;
(LXX+WH+) καιG2532 CONJ εδωκενG1325 V-AAI-3S δαυιδN-PRI σαλωμωνN-PRI τωG3588 T-DSM υιωG5207 N-DSM αυτουG846 D-GSM τοG3588 T-ASN παραδειγμαN-ASN τουG3588 T-GSM ναουG3485 N-GSM καιG2532 CONJ τωνG3588 T-GPM οικωνG3624 N-GPM αυτουG846 D-GSM καιG2532 CONJ τωνG3588 T-GPM ζακχωN-PRI αυτουG846 D-GSM καιG2532 CONJ τωνG3588 T-GPN υπερωωνG5253 N-GPN καιG2532 CONJ τωνG3588 T-GPF αποθηκωνG596 N-GPF τωνG3588 T-GPM εσωτερωνG2082 A-GPMC καιG2532 CONJ τουG3588 T-GSM οικουG3624 N-GSM τουG3588 T-GSM εξιλασμουN-GSM
(Vulgate) dedit autem David Salomoni filio suo descriptionem porticus et templi et cellariorum et cenaculi et cubiculorum in adytis et domus propitiationis
Domus propitiationis = house of graciousness, house of conciliation.
H3727
כּפּרת
kappôreth
BDB Definition:
1) mercy-seat, place of atonement
1a) the golden plate of propitiation on which the High Priest sprinkled the seat 7 times on the Day of Atonement symbolically reconciling Jehovah and His chosen people
1a1) the slab of gold on top of the ark of the covenant which measured 2.5 by 1.5 cubits; on it and part of it were the two golden cherubim facing each other whose outstretched wings came together above and constituted the throne of God
Part of Speech: noun feminine
A Related Word by BDB/Strong’s Number: from H3722
H3722
כּפר
kâphar
BDB Definition:
1) to cover, purge, make an atonement, make reconciliation, cover over with pitch
1a) (Qal) to coat or cover with pitch
1b) (Piel)
1b1) to cover over, pacify, propitiate
1b2) to cover over, atone for sin, make atonement for
1b3) to cover over, atone for sin and persons by legal rites
1c) (Pual)
1c1) to be covered over
1c2) to make atonement for
1d) (Hithpael) to be covered
Part of Speech: verb
A Related Word by BDB/Strong’s Number: a primitive root
G2435
ἱλαστήριον
hilastērion
hil-as-tay'-ree-on
Neuter of a derivative of G2433; an expiatory (place or thing), that is, (concretely) an atoning victim, or (specifically) the lid of the Ark (in the Temple): - mercyseat, propitiation.
G2433
ἱλάσκομαι
hilaskomai
hil-as'-kom-ahee
Middle voice from the same as G2436; to conciliate, that is, (transitively) to atone for (sin), or (intransitively) be propitious: - be merciful, make reconciliation for.
G2435
ἱλαστήριον
hilastērion
Thayer Definition:
1) relating to an appeasing or expiating, having placating or expiating force, expiatory; a means of appeasing or expiating, a propitiation
1a) used of the cover of the ark of the covenant in the Holy of Holies, which was sprinkled with the blood of the expiatory victim on the annual day of atonement (this rite signifying that the life of the people, the loss of which they had merited by their sins, was offered to God in the blood as the life of the victim, and that God by this ceremony was appeased and their sins expiated); hence the lid of expiation, the propitiatory
1b) an expiatory sacrifice
1c) a expiatory victim
Part of Speech: noun neuter
A Related Word by Thayer’s/Strong’s Number: from a derivative of G2433
G2433
ἱλάσκομαι
hilaskomai
Thayer Definition:
1) to render one’s self, to appease, conciliate to one’s self
1a) to become propitious, be placated or appeased
1b) to be propitious, be gracious, be merciful
2) to expiate, make propitiation for
Part of Speech: verb
A Related Word by Thayer’s/Strong’s Number: middle voice from the same as G2436
Num 7:89 And when MosesH4872 was goneH935 intoH413 the tabernacleH168 of the congregationH4150 to speakH1696 withH854 him, then he heardH8085 (H853) the voiceH6963 of one speakingH1696 untoH413 him from offH4480 H5921 the mercy seatH3727 thatH834 was uponH5921 the arkH727 of testimony,H5715 from betweenH4480 H996 the twoH8147 cherubims:H3742 and he spakeH1696 untoH413 him.
Shalom