aiphnidios describes an event arriving without warning, as in destruction or an awaited day.

The two occurrences describe an event that comes without warning: destruction in 1 Thessalonians 5:3 and “that day” in Luke 21:34. The differing gender of the adjective follows the nouns in their respective clauses rather than marking separate uses.

1. Arriving without warning · dominant

   In 1 Thessalonians 5:3, the nominative masculine form modifies the destruction said to come when people say, “Peace and security”; the APB renders the clause “then sudden destruction will come upon them.” In Luke 21:34, the nominative feminine form occurs where “that day” is warned against coming upon hearers; the APB renders it “that day come upon you suddenly.”

   1 Thessalonians 5:3Luke 21:34

In the Anselm Project Bible: The APB uses “sudden” with “destruction” in 1 Thessalonians 5:3 and “suddenly” with the coming of “that day” in Luke 21:34. These renderings confirm the clauses' presentation rather than isolate the term mechanically.