Apostasy (greek: αποστασία — backsliding, falling away) — to depart from the faith (1Ti 4:1), betrayal of the Christian faith, to fall away (Luk.8:13), a falling away (2Th.2:3), departing from the living God (Hbr.3:12).
In the New Testament «apostasy» means the departure from the Christian faith (2Th.2:3, Luk.8:13, 1Ti.4:1-3, Hbr.3:12, 2Pe.2:20, 2Pe.3:17).
In Septuagint, The Greek Old Testament, word «apostasy» means the departure from God (Jos.22:22, 2Ch.29:19, Jer.2:19, Hsa.11:7).
Since the time of Cyprian, bishop of Carthage, in early Christian Church we may find concept of the apostate, greek: αποστατης — apostates (plural). Apostates are those who renounce their Christian faith in the time of persecutions (Luk.8:13).
Lapsi was also the name given to some apostates because they have lapsed or fallen away from their faith and decide later in life to come back to it.
Word «αποστασία» in the New Testament
3 Let no man deceive you by any means: for [that day shall not come], except there come a falling away (ἡ ἀποστασία) first, and that man of sin be revealed, the son of perdition;
4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
21 And they are informed of thee, that thou teachest all the Jews which are among the Gentiles to forsake (ἀποστασίαν) Moses , saying that they ought not to circumcise [their] children, neither to walk after the customs.
13 а They on the rock [are they], which, when they hear, receive the word with joy; and these have no root, which for a while believe, and in time of temptation fall away. (ἀφίστανται);
1 Now the Spirit speaketh expressly, that in the latter times some shall depart from the faith (ἀποστήσονταί τινες τῆς πίστεως), giving heed to seducing spirits, and doctrines of devils;
2 Speaking lies in hypocrisy; having their conscience seared with a hot iron;
3 Forbidding to marry, [and commanding] to abstain from meats, which God hath created to be received with thanksgiving of them which believe and know the truth.
12 Take heed, brethren, lest there be in any of you an evil heart of unbelief (καρδία πονηρὰ ἀπιστίας), in departing (τῷ ἀποστῆναι) from the living God.
20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome , the latter end is worse with them than the beginning.
21 For it had been better for them not to have known the way of righteousness, than, after they have known [it], to turn from the holy commandment delivered unto them.
17 Ye therefore, beloved, seeing ye know [these things] before, beware lest ye also, being led away with the error of the wicked (τῇ τῶν ἀθέσμων πλάνῃ), fall (ἐκπέσητε) from your own stedfastness.
Word «αποστασία» in the Old Testament
22 The LORD God of gods, the LORD God of gods, he knoweth, and Israel he shall know; if [it be] in rebellion, or if in transgression (ἐν ἀποστασίᾳ) against the LORD, (save us not this day,)
18 Then they went in to Hezekiah the king, and said, We have cleansed all the house of the LORD, and the altar of burnt offering, with all the vessels thereof, and the shewbread table, with all the vessels thereof.
19 Moreover all the vessels, which king Ahaz in his reign did cast away in his transgression (ἐν τῇ ἀποστασίᾳ), have we prepared and sanctified, and, behold, they [are] before the altar of the LORD.
19 Thine own wickedness shall correct thee, and thy backslidings (ἡ ἀποστασία) shall reprove thee: know therefore and see that [it is] an evil [thing] and bitter, that thou hast forsaken the LORD thy God, and that my fear [is] not in thee, saith the Lord GOD of hosts.
19 And my people are bent to backsliding (משובה) from me: though they called them to the most High, none at all would exalt [him].