Definitions

1. verb

to make a low, continuous humming or rumbling sound, typically with the larynx, as an animal does when it is content or sleepy

“The cat began to purr as it sat on my lap.”

2. noun

the sound made by a cat, especially when it is content or sleepy

“The purr of the cat filled the room.”

3. verb, intransitive

to be in a state of quiet contentment or satisfaction

“The baby started to purr as she was rocked to sleep.”