径 (jìng) has three distinct senses you'll encounter at an advanced level. As a noun, it means a narrow path or footpath (小径). In mathematics, it's the diameter (直径), used in geometry and measurements. As an adverb, it means 'directly' or 'straight', often in literary or formal contexts (径直). The POS tag in some dictionaries may label it as a classifier, but in actual usage it functions primarily as a noun or adverb.