That can be knitted or used as material for knitting.(adjective)
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Use "knittable" in a sentence
"Knitting Vintage Socks by Nancy Bush has caused whoops of delight and much frantic winding of my Yarn Yard skeins of the month into knittable balls of wool in readiness."
"While she always has a great sense of what's pretty and knittable, this time, she totally hit it--the new stuff is gorgeous."
"And knittable: crafty bloggers can check out the "extermiknit" pattern here."