Classical-only reading. In modern Mandarin, 'to tell' is 告诉 — yù survives only in literary fragments and idioms quoting old texts. Encountered mostly when reading the Analects or pre-Qin philosophy. Don't use it in spoken Chinese.
history
Confucius famously said 吾语女 'I will tell you' (Analects, 阳货 chapter). Same character, same writing — only the tone flips from yǔ (noun: speech) to yù (verb: to tell).
Left speech radical, simplified side-form of 言. Frames this rare reading as still a speech-act: yù = 'to convey words to someone'. The radical is unchanged between the yǔ and yù readings — only the tone distinguishes them.
Phonetic 吾 on the right. Both readings (yǔ, yù) descend from the same wú-series sound family. The yù reading represents an old causative-style tone shift in classical Chinese: speech (yǔ) becomes to cause-to-hear, to tell (yù). The graph stays identical.
