To pronounce a sound with the nasal passages open, allowing air to escape through the nose. In French, speakers often nasalize vowels in certain words.
To give (a sound or voice) a nasal quality; to speak or sing in a nasal tone. When he imitated the comedian, he deliberately nasalized his voice.
To mark (a letter or syllable) with a sign indicating nasalization. The linguist nasalized the vowel by adding a tilde in the transcription.