Old English heofon "home of God," earlier "sky, firmament," probably from Proto-Germanic *hibin-, dissimilated from *himin- (cf. Low German heben, Old Norse himinn, Gothic himins, Old Frisian himul, Dutch hemel, German Himmel "heaven, sky"), perhaps from PIE root *kem-/*kam- "to cover" (cf. chemise). [Watkins derives it elaborately from PIE *ak- "sharp" via *akman- "stone, sharp stone," then "stony vault of heaven"].
Plural use in sense of "sky" is probably from Ptolemaic theory of space composed of many spheres, but it also formerly was used in the same sense as the singular in Biblical language, as a translation of Hebrew plural shamayim. Heaven-sent (adj.) attested from 1640s.
(1.) Definitions. The phrase "heaven and earth" is used to indicate the whole universe (Gen. 1:1; Jer. 23:24; Acts 17:24). According to the Jewish notion there were three heavens, (a) The firmament, as "fowls of the heaven" (Gen. 2:19; 7:3, 23; Ps. 8:8, etc.), "the eagles of heaven" (Lam. 4:19), etc. (b) The starry heavens (Deut. 17:3; Jer. 8:2; Matt. 24:29). (c) "The heaven of heavens," or "the third heaven" (Deut. 10:14; 1 Kings 8:27; Ps. 115:16; 148:4; 2 Cor. 12:2). (2.) Meaning of words in the original, (a) The usual Hebrew word for "heavens" is _shamayim_, a plural form meaning "heights," "elevations" (Gen. 1:1; 2:1). (b) The Hebrew word _marom_ is also used (Ps. 68:18; 93:4; 102:19, etc.) as equivalent to _shamayim_, "high places," "heights." (c) Heb. galgal, literally a "wheel," is rendered "heaven" in Ps. 77:18 (R.V., "whirlwind"). (d) Heb. shahak, rendered "sky" (Deut. 33:26; Job 37:18; Ps. 18:11), plural "clouds" (Job 35:5; 36:28; Ps. 68:34, marg. "heavens"), means probably the firmament. (e) Heb. rakia is closely connected with (d), and is rendered "firmamentum" in the Vulgate, whence our "firmament" (Gen. 1:6; Deut. 33:26, etc.), regarded as a solid expanse. (3.) Metaphorical meaning of term. Isa. 14:13, 14; "doors of heaven" (Ps. 78:23); heaven "shut" (1 Kings 8:35); "opened" (Ezek. 1:1). (See 1 Chr. 21:16.) (4.) Spiritual meaning. The place of the everlasting blessedness of the righteous; the abode of departed spirits. (a) Christ calls it his "Father's house" (John 14:2). (b) It is called "paradise" (Luke 23:43; 2 Cor. 12:4; Rev. 2:7). (c) "The heavenly Jerusalem" (Gal. 4: 26; Heb. 12:22; Rev. 3:12). (d) The "kingdom of heaven" (Matt. 25:1; James 2:5). (e) The "eternal kingdom" (2 Pet. 1:11). (f) The "eternal inheritance" (1 Pet. 1:4; Heb. 9:15). (g) The "better country" (Heb. 11:14, 16). (h) The blessed are said to "sit down with Abraham, Isaac, and Jacob," and to be "in Abraham's bosom" (Luke 16:22; Matt. 8:11); to "reign with Christ" (2 Tim. 2:12); and to enjoy "rest" (Heb. 4:10, 11). In heaven the blessedness of the righteous consists in the possession of "life everlasting," "an eternal weight of glory" (2 Cor. 4:17), an exemption from all sufferings for ever, a deliverance from all evils (2 Cor. 5:1, 2) and from the society of the wicked (2 Tim. 4:18), bliss without termination, the "fulness of joy" for ever (Luke 20:36; 2 Cor. 4:16, 18; 1 Pet. 1:4; 5:10; 1 John 3:2). The believer's heaven is not only a state of everlasting blessedness, but also a "place", a place "prepared" for them (John 14:2).