twilight zone

American  

noun

1. the lowest level of the ocean that light can reach.

2. an ill-defined area between two distinct conditions, categories, etc., usually comprising certain features of both; an indefinite boundary.

   a twilight zone between fantasy and reality.

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twilight zone British  

noun

1. any indefinite or transitional condition or area

2. an area of a city or town, usually surrounding the central business district, where houses have become dilapidated

3. the lowest level of the ocean to which light can penetrate

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Etymology

Origin of twilight zone

First recorded in 1905–10

Example Sentences

Twilight zone animals play a major part in the carbon cycle, bringing organic carbon from surface waters and trapping them deep beneath the tides.

From Science Magazine • Jul. 2, 2021