(exp.) a phrase uttered when told old news, or to express that you know more about a subject than the person explaining it to you
Considering how useful this one is, it’s a surprise it’s ever fallen out of fashion. In Tudor period English (we’re talking late Middle English–Early Modern English, if you want to be more specific), yes, hazelwood! was a means of pointing out that you’re already aware of something you’ve just been told, or want to show that you know more about it than the person telling you it.
That’s an expression from a 1914 Glossary of Tudor and Stuart Words by the acclaimed lexicographer Walter Skeat. As he goes on to explain:
The exclamation implies that the information given is of a very simple description, and that the hearer knows a great deal more of the matter than the informant.
So where does it come from? Happily, Skeat tells us this tale too.
He might be best known for the Canterbury Tales, but in the mid 1380s, Geoffrey Chaucer tried his hand at retelling the legend of Troilus and Cressida too. His version of their tale includes the line, “Yea, hasel-wodes shaken!”—implying, in other words, that hazel trees shake when the wind blows through them:
“A ring?” quod he, “Ye, hasel-wodes shaken!
Ye nece myn, that ring moste han a stoon
That mighte dede men alyve maken;
And swich a ring trowe I that ye have noon.
Chaucer, Troilus and Criseyde (c. 1385)
Clearly, pointing out that trees move in the wind is nothing startling, nor new information—and it’s from there that this phrase came to be used on hearing old news, or when being patronized by someone who apparently thinks you don’t know what you’re talking about.
Was it Chaucer’s invention, or was it widely known before he wrote it down some six-and-a-half centuries ago? Without further evidence, we’ll never know.