"whirrs" in the noun sense
1. whir, whirr, whirring, birr
sound of something in rapid motion
"whir of a bird's wings"
"the whir of the propellers"
"whirrs" in the verb sense
1. whizz, whiz, whirr, whir, birr, purr
make a soft swishing sound
"the motor whirred"
"the car engine purred"
2. churr, whirr
make a vibrant sound, as of some birds
Source: WordNet® (An amazing lexical database of English)
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