1. Gentle utterance use to call someone's attention
   - ahem, hem 
2. Exclamation expressing doubt, deliberation, dissent, or hesitation
   - hum, ahem

Encyclopedia: Hmm

• night raven
• night school
• night shift
• night snake
• night soil
• night table
• night terror
• night vision
• night watch
• night watchman
• night-blooming cereus
• night-light
• night-line
• night-robe
• night-sight
• night-stop
• nightbird
• nightcap
• nightclothes
• nightclub
• nightcrawler
• nightdress
• nighted
• nightfall
• nightgown