swingle (n.)

"instrument for beating flax," early 14c., from Middle Dutch swinghel "swingle for flax," cognate with Old English swingell "beating, stick to beat, whip, scourge, rod," from swingan "to beat, strike, whip" (see swing (v.)) + instrumental suffix -el (1). Or perhaps directly from the Old English word, with narrowing of sense.