thief in the night

A calque from Ancient Greek κλέπτης ἐν νυκτί (kléptēs en nuktí).

• IPA^(key): /θiːf ɪn ðə naɪt/

• Audio (General Australian):

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thief in the night (plural thieves in the night)

1. Something stealthy or that occurs without warning.
   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC, 1 Thessalonians 5:2:

     For yourselves know perfectly that the day of the Lord so cometh as a thief in the night.

• Mostly used in similes, after like.