Jehovah
The special and significant name (not merely an appellative title such as Lord) by which God revealed himself to the ancient Hebrews (Exo_6:2, Exo_6:3). This name, the Tetragrammaton of the Greeks, was held by the later Jews to be so sacred that it was never pronounced except by the high priest on the great Day of Atonement, when he entered into the most holy place. Whenever this name occurred in the sacred books they pronounced it, as they still do, “Adonai” (i.e., Lord), thus using another word in its stead. The Massorets gave to it the vowel-points appropriate to this word. This Jewish practice was founded on a false interpretation of Lev_24:16. The meaning of the word appears from Exo_3:14 to be “the unchanging, eternal, self-existent God,” the “I am that I am,” a covenant-keeping God. (Compare Mal_3:6; Hos_12:5; Rev_1:4, Rev_1:8.)
The Hebrew name “Jehovah” is generally translated in the Authorized Version (and the Revised Version has not departed from this rule) by the word LORD printed in small capitals, to distinguish it from the rendering of the Hebrew Adonai and the Greek Kurios, which are also rendered Lord, but printed in the usual type. The Hebrew word is translated “Jehovah” only in Exo_6:3; Psa_83:18; Isa_12:2; Isa_26:4, and in the compound names mentioned below.
It is worthy of notice that this name is never used in the LXX., the Samaritan Pentateuch, the Apocrypha, or in the New Testament. It is found, however, on the “Moabite stone” (q.v.), and consequently it must have been in the days of Mesba so commonly pronounced by the Hebrews as to be familiar to their heathen neighbours.

G86
ᾅδης
hadēs
Thayer Definition:
1) name Hades or Pluto, the god of the lower regions
2) Orcus, the nether world, the realm of the dead
3) later use of this word: the grave, death, hell

From G1 (as a negative particle) and G1492; properly unseen, that is, “Hades” or the place (state) of departed souls: - grave, hell
(Strong's)

in hell — not the final place of the lost (for which another word is used), but as we say “the unseen world.”
(JFB)