Onomatopoeia
Onomatopoeiac monosyllables may be extended without limit to represent a long drawn-out sound or utterance. For example, Yann Martel's 1995 novel Self includes 45-letter Ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh and 35-letter Ooooooooooooooooooooooooooooooooooh.
Read more about this topic: List Of The Longest English Words With One Syllable