liedetector

WordReference Random House Learner's Dictionary of American English © 2026

lie de•tec•tor /ˈlaɪ dɪˌtɛktɚ/  n. [countable]

1. an instrument that records the changes in certain activities of a person's body that may indicate when a lie is being told.

Also called polygraph. 

WordReference Random House Unabridged Dictionary of American English © 2026

lie′ detec′tor, 

1. a polygraph used to determine changes in certain body activities, as blood pressure, pulse, breathing, and perspiration, the results of which may be interpreted to indicate the truth or falsity of a person's answers under questioning.

• 1905–10, American.

Collins Concise English Dictionary © HarperCollins Publishers::

lie detector noun

1. a polygraph used esp by a police interrogator to detect false or devious answers to questions, a sudden change in one or more involuntary physiological responses being considered a manifestation of guilt, fear, etc
   See polygraph1