Not that hoary old chestnut (=old idea, joke, remark etc) again.hoaryhoar‧y /ˈhɔːri/ adjective 
Not that hoary old chestnut (=old idea, joke, remark etc) again.2 old-fashioned grey or white in colour, especially through age
WORD ORIGINhoary
Origin:
1500-1600 hoar; ➔ HOARFROSTEXAMPLES FROM OTHER DICTIONARIES
- a hoary 1940s musical
- All the grass in front was brittle and hoary white.
- At least one House Republican freshman maintains a hoary political tradition by staging town meetings with his constituents.
- Attractive hoary foliage, and brilliant scarlet orange flowers.
- For a female swimmer, 29-year-old Angel Martino is downright hoary.
- It contains many majestic old oaks and hoary willows.
- Then bring her back inside, complete with Groucho Marx cigar, to run through a repertoire of hoary Borscht-belt gags.
COLLOCATIONS FROM THE ENTRY Not that hoary old chestnut (=old idea, joke, remark etc) again.
1[usually before noun] a hoary joke, remark etc is so well known that people no longer find it amusing or interesting: Not that hoary old chestnut (=old idea, joke, remark etc) again. Not that hoary old chestnut (=old idea, joke, remark etc) again.2 old-fashioned grey or white in colour, especially through age