knife的復數形式為knives。
knife遵循可數名詞復數變化規則：以f或fe 結尾的名詞，先去f，fe，再加ves。half-halves、knife-knives、leaf-leaves、wolf-wolves、wife-wives、life-lives、thief-thieves。
另外有些單詞以f或fe 結尾加s，例如：belief-beliefs、roof-roofs、safe-safes、gulf-gulfs。
knife的意思：
n.
1、小刀；餐刀；菜刀。
2、短刀；匕首。
3、（機械工程）刃部；（機器上的）刀具，刀片。
4、（外）手術刀。
vt.
1、拿小刀切；拿尖刀戳。
2、（口語）秘密打擊；用陰險手段擊敗；背叛。
3、刀切似地穿過。
4、用括刀塗（顏料等）。
vi.
（刀似地）劈開，穿過。
例句：
1、Deng said she pulled out a knife after the men repeatedly dragged her back as she tried to leave.
鄧玉嬌說她極力想離開，那幾名男子卻壹再把她往後拉，她就拔出了刀子。
2、Calmly, the man withdrew a small knife from his pocket and carved a mark on the boat at the spot where he dropped the sword.
那個人不慌不忙地從衣袋裏取出壹個小刀，在船舷上落下寶劍的地方刻了壹個記號。
3、There was blood on the painted feet, as though the thing had dripped-blood even on the hand that had not held the knife.
畫中人那腳上還有血跡——甚至好像連沒有拿過刀的手也在淌血。
4、He went to a rotten log near at hand and began to dig under one end of it with his Barlow knife.
他走到近處的壹根爛樹幹旁邊，開始用他的巴露折刀在壹頭開挖起來。