Plain English Meaning
The marked face of a gauge or instrument that you read to see what value it is showing.
Full Definition
The face of an instrument, marked with numbers, graduations, or symbols, against which a pointer or indicator is read to display a measured value.
Context Anchor
Seen on cockpit instruments such as altimeters, airspeed indicators, pressure gauges, and heading indicators.
Derivation
From the Latin 'dies' meaning 'day,' originally referring to a sundial -- a marked face used to read the position of the sun's shadow. The meaning extended to any marked face used with a pointer to show a measurement.
Why Pilots Care
Pilots must read instrument dials correctly because a wrong reading can lead to poor decisions about altitude, speed, fuel, engine condition, or aircraft direction.
Intuition Check
Do not read dial here as a phone control or only as the act of selecting a setting. In this instrument sense, the dial is the marked face you read.
Example Sentence 1
He set the desired altitude by turning the knob until the number appeared in the window on the dial.
Example Sentence 2
Vibration caused the needle on the fuel quantity dial to flicker during the climb.