third-person singular simple present of hum

• produces a low, continuous sound
• sings a wordless tune with closed lips
• is busy and vibrant, like a beehive

plural of hum

• low, continuous sounds or background drones
• short wordless tunes
• bustle of activity, like a beehive

plural of HUM (“Highly Unusual Methods”) in contract bridge

• unconventional bidding systems requiring prior disclosure