The noun 剑 (jiàn) refers to a sword, specifically the double-edged straight sword traditional in Chinese culture. It is one of the most iconic weapons in Chinese martial arts and literature. The measure word for swords is 把 (bǎ), as in 一把剑.
他从小就喜欢练剑,现在已经是高手了。
Tā cóngxiǎo jiù xǐhuan liàn jiàn, xiànzài yǐjīng shì gāoshǒu le.
He has loved practicing swordsmanship since he was young, and now he's already an expert.
墙上挂着一把剑,看起来很有年代感。
Qiáng shàng guàzhe yī bǎ jiàn, kàn qǐlái hěn yǒu niándài gǎn.
A sword hangs on the wall, looking very antique.
师父送给他一把剑,让他好好练习。
Shīfu sòng gěi tā yī bǎ jiàn, ràng tā hǎohǎo liànxí.
The master gave him a sword and told him to practice diligently.