From Old English 'hlysnan,' from PIE *klew- (to hear) — distantly related to 'loud,' an ancient family of hearing words.
To give one's attention to a sound; to make an effort to hear something; to pay attention to advice or a request.
From Old English 'hlysnan' meaning 'to listen, to hear,' from Proto-Germanic *hlusnijaną or *hlusinōną (to listen), from PIE root *ḱlew- (to hear). The same PIE root gave Greek 'klyein' (to hear), Latin 'cluēre' (to be called, to be reputed), and Sanskrit 'śṛṇoti' (he hears). The initial cluster /hl-/ in Old English was simplified to /l-/ during the Middle English period, one of many consonant cluster reductions that transformed English pronunciation. Key
The silent 't' in 'listen' was not always silent — Old English 'hlysnan' gained an inserted 't' during the Middle English period (becoming 'listnen') for ease of pronunciation between /s/ and /n/, the same process that put a 't' into 'hasten,' 'fasten,' 'glisten,' and 'moisten.' But then English pronunciation changed direction and dropped the very /t/ it had inserted, leaving only the spelling as a fossil.