Greek word
aiphnídios
αἰφνίδιος
What it means
unexpected, i.e. suddenly
unexpected, i.e. (adverbially) suddenly
Where it comes from
from a compound of A (Α) (as a negative particle) and phaínō (φαίνω) (compare exaíphnēs (ἐξαίφνης)) (meaning non-apparent)
How the King James translates it
Every place it appears 1
1 Thessalonians5:3