Quick Definition
unexpected, sudden
Strong's Definition
unexpected, i.e. (adverbially) suddenly
Derivation: from a compound of G1 (Α) (as a negative particle) and G5316 (φαίνω) (compare G1810 (ἐξαίφνης)) (meaning non-apparent);
KJV Usage: sudden, unawares
Thayer's Greek Lexicon
αἰφνίδιος, (αἰφνης, ἀφανής, ἄφνω, which see), unexpected, sudden, unforeseen: Luk_21:34 (here WH ἐφνιδ., see their Introductory § 404 and Appendix, p. 151); 1Th_5:8. (Wis_17:14; 2Ma_14:17; 3Ma_3:24; Aeschylus, Thucydides 2, 61 τό αἰφνίδιον καί ἀπροσδόκητον, Polybius, Josephus, Plutarch, Dionysius Halicarnassus, others.)
STRONGS NT 160: ἐφνιδιος [ἐφνιδιος, see αἰφνίδιος.]
Mounce Concise Greek Dictionary
αἰφνίδιος aiphnidios 2x
unforeseen, unexpected, sudden, Luk_21:34 ; 1Th_5:3
Abbott-Smith Greek Lexicon
** αἰφνίδιος
(in Lk, l.c ., ἐφν - WH ; v. M , Pr., 35), -ον
( <αἴφνης = ἄφνως , suddenly ),
[in LXX : Wis_17:15 , 2Ma_14:17 , 3Ma_3:24 * ;]
sudden unexpected: Luk_21:34 , 1Th_5:3 .†
ἐφνίδιος , see αἰφνίδιος .
Moulton & Milligan — Vocabulary of the Greek NT
αἰφνίδιος [page 16]
The adverb occurs in P Fay 123 .21 ff. ( c. A.D. 100), an uneducated letter αἰφνιδί [.]ως (with a letter erased) εἴρηχεν ἡμῖν σήμερον : cf. Syll 324 .20 (i/B.C.) αἰφνίδιον σ (υ )μφορὰν θεασάμενος , also ib. 326 .7 αἰφνιδίως ἐπιβαλόντος and OGIS 339 .18 (ii/B.C.) ἐκ τῆς αἰφνιδίου περιστάσεως .
Liddell-Scott — Intermediate Greek Lexicon
αἰφνίδιος [Etym: ἄφνω] "unforeseen, sudden", Aesch. , Thuc. :—adv. -ίως, Id=Thuc. ; also -ιον Plut.
STEPBible — Tyndale Abridged Greek Lexicon
αἰφνίδιος (in Lk, l.with, ἐφν- WH; see M, Pr., 35), -ον
(αἴφνης = ἄφνως, suddenly), [in LXX: Wis.17:15, 2Ma.14:17, 3Ma.3:24 * ;]
sudden, unexpected: Luk.21:34, 1Th.5:3.†
(AS)
📖 In-Depth Word Study
Suddenly (160) aiphnidios
Suddenly (160)(aiphnidios from aÃphnes = unexpected, sudden) describes that which is unexpected or unforeseen. It is something that one cannot anticipate nor understand how it happened.
In the present verse aiphnidios is at the beginning of the sentence for emphasis and refers to the sudden, unexpected, unforeseen destruction accompanying the last 3.5 year period referred to as the Great Tribulation (Mt 24:21), the time of Jacob's distress or trouble (Jeremiah 30:7 "Alas! for that day is great, There is none like it; And it is the time of Jacob's distress, But he will be saved from it.") or the time of distress in (Daniel 12:1 "...And there will be a time of distress such as never occurred since there was a nation until that time; and at that time your people, everyone who is found written in the book, will be rescued.")
The only other NT use of aiphnidios is in Luke 21:34 (click discussion of this verse).
Suddenly stands emphatically at the beginning of the sentence.
MacDonald comments on this fateful time writing that...
There will be an air of confidence and security in the world. Then God’s judgment will suddenly begin to descend with vast destructive force. Destruction does not mean loss of being, or annihilation; it means loss of well-being, or ruin as far as the purpose of one’s existence is concerned. It will be as inevitable and unavoidable as labor pains upon a pregnant woman. From this judgment there will be no escape for unbelievers. (MacDonald, W & Farstad, A. Believer's Bible Commentary: Thomas Nelson or Logos)
"Copy and paste the address below into your web browser in order to go to the original page which will allow you to access live links related to the material on this page - these links include Scriptures (which can be read in context), Scripture pop-ups on mouse over, and a variety of related resources such as Bible dictionary articles, commentaries, sermon notes and theological journal articles related to the topic under discussion."
http://www.preceptaustin.org/1thessalonians_51-3.htm#suddenly