A blip on a polygraph is an indication of a LIE. The crossword solutions for this term are LIE (3 letters), RADAR (5 letters), ECHO (4 letters), LIES (4 letters), LIAR (4 letters), LYING (5 letters), and SONAR (5 letters). LIE is a verb meaning to tell an untruth, while RADAR, ECHO, SONAR, and LYING are all related to the detection of LIES. RADAR and SONAR are both forms of electronic detection used to detect objects or people, while ECHO is an acoustic signal used to detect objects underwater. LIES and LIAR are both nouns referring to someone who tells untruths.