'Son of God' definitions:

Definition of 'Son of God'

Son of God The plural, "sons of God," is used (Gen. 6:2, 4) to denote the pious descendants of Seth. In Job 1:6; 38:7 this name is applied to the angels. Hosea uses the phrase (1:10) to designate the gracious relation in which men stand to God.
In the New Testament this phrase frequently denotes the relation into which we are brought to God by adoption (Rom. 8:14, 19; 2 Cor. 6:18; Gal. 4:5, 6; Phil. 2:15; 1 John 3:1, 2). It occurs thirty-seven times in the New Testament as the distinctive title of our Saviour. He does not bear this title in consequence of his miraculous birth, nor of his incarnation, his resurrection, and exaltation to the Father's right hand. This is a title of nature and not of office. The sonship of Christ denotes his equality with the Father. To call Christ the Son of God is to assert his true and proper divinity. The second Person of the Trinity, because of his eternal relation to the first Person, is the Son of God. He is the Son of God as to his divine nature, while as to his human nature he is the Son of David (Rom. 1:3, 4. Comp. Gal. 4:4; John 1:1-14; 5:18-25; 10:30-38, which prove that Christ was the Son of God before his incarnation, and that his claim to this title is a claim of equality with God).
When used with reference to creatures, whether men or angels, this word is always in the plural. In the singular it is always used of the second Person of the Trinity, with the single exception of Luke 3:38, where it is used of Adam.