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

Encyclopedia: Hmm

• unenlightenment
• unenlivened
• unenterprising
• unenthusiastic
• unenthusiastically
• unentitled
• unenviable
• unequable
• unequal
• unequal to
• unequaled
• unequalised
• unequalized
• unequalled
• unequally
• unequipped
• unequitable
• unequivocal
• unequivocally
• unequivocalness
• unerasable
• wine waiter
• wine-colored
• wine-coloured
• wine-maker's yeast