lengthen Syllabification: (length·en)Pronunciation: /ˈleNG(k)THən, ˈlen-/Translate lengthen | into French | into German | into Italian | into Spanish Definition of lengthen verb make or become longer: [with object]:she lengthened her stride to catch up [no object]:in the spring when the days are lengthening (as adjective lengthening)the lengthening shadows [with object] Prosody & Phonetics make (a vowel or syllable) long. lengthen in other Oxford dictionaries Definition of lengthen in the British & World English dictionary