hum
/ˈhum/ · B2 · intj
synonym of uf
Sounds like a sigh-grunt: hum = Spanish 'uf', a huffed hesitation
Spanish hum is an interjection like uf, voiced with lips closed in a short hum. Hear it as a doubtful or tired murmur: the same sound English speakers make when unsure, so hum and 'hmm' share one meaning.