a stiff hollow protective spine on a porcupine or hedgehog
"The baby porcupine carefully wiggled its way out of the burrow, leaving a trail of fallen quills behind it."
any of the larger wing or tail feathers of a bird
"The eagle carefully plucked its large quills before taking flight to ensure they wouldn't tangle in the wind."
The lower shaft of a feather, specifically the region lacking barbs.
"The artist carefully trimmed the quill from the goose feather before dipping it into the inkwell to begin his sketch."
To pierce or be pierced with quills.
"The porcupine stepped forward and immediately began to defend itself, causing its sharp quills to pierce through the hunter's sleeve."
A surname.
"The local history club invited Mr. Quill to speak about the town's early settlers."