dew-point

The dew-point is reached when morning fog forms over the meadow.

Definition

1. Noun (countable, usually singular):
   • Meteorological term: The "dew-point" (or "dew point") is the temperature to which air must be cooled, at a constant pressure and water vapor content, in order for it to become saturated and for water vapor to condense into liquid water (dew). It is a measure of atmospheric moisture.

Usage Examples

• (The temperature at which condensation begins.)
• (The specific threshold for moisture condensation.)
• (A measure of humidity in the air.)

Advanced Usage

• "Dew-point depression": the difference between the ambient air temperature and the dew-point temperature. A large depression indicates dry air; a small depression indicates humid air.

  • A dew-point depression of 2°C suggests the air is nearly saturated. (A small difference means high humidity.)

• "Dew-point hygrometer": an instrument that measures the dew-point temperature by cooling a surface until condensation appears.

  • The meteorologist used a dew-point hygrometer to record moisture levels. (A device for precise humidity measurement.)

Variants and Related Words

• Dew (n): water droplets that form on cool surfaces at night when the air temperature reaches the dew-point.

  • The grass was wet with morning dew. (Condensed moisture from the air.)

• Frost point (n): the temperature at which water vapor deposits directly as ice (below 0°C), analogous to the dew-point for liquid water.

  • The frost point was -5°C, so frost formed on the windows. (The ice-formation equivalent of the dew-point.)

Synonyms

• Condensation point: the temperature at which water vapor changes to liquid.
• Saturation temperature: the temperature at which air becomes fully saturated with water vapor.

Related Idioms and Phrases

• "At the dew-point": used figuratively to describe a critical threshold or moment of change.
  • The argument reached its dew-point when tempers finally flared. (The point at which tension turned into conflict.)