listen (n.) Look up listen at
"an act of listening," 1788, in on the listen "alert," from listen (v.).
listen (v.) Look up listen at
Old English hlysnan (Northumbrian lysna) "to listen, hear; attend to, obey" (transitive), from Proto-Germanic *khlusinon (source also of Dutch luisteren, Old High German hlosen "to listen," German lauschen "to listen"), from PIE root *kleu- "hearing, to hear."

This root is the source also of Sanskrit srnoti "hears," srosati "hears, obeys;" Avestan sraothra "ear;" Middle Persian srod "hearing, sound;" Lithuanian klausau "to hear," slove "splendor, honor;" Old Church Slavonic slusati "to hear," slava "fame, glory," slovo "word;" Greek klyo "hear, be called," kleos "report, rumor, fame glory," kleio "make famous;" Latin cluere "to hear oneself called, be spoken of;" Old Irish ro-clui-nethar "hears," clunim "I hear," clu "fame, glory," cluada "ears;" Welsh clywaf "I hear;" Old English hlud "loud," hleoðor "tone, tune;" Old High German hlut "sound;" Gothic hiluþ "listening, attention."

The -t- probably is by influence of Old English hlystan (see list (v.2)). For vowel evolution, see bury. Intransitive sense is from c. 1200. To listen in (1905) was originally in reference to radio broadcasts.