The most common and most likely answer to this crossword clue is the 8 letter word PREMOLAR
I've seen this crossword clue in The Times
P
R
E
M
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Buddy explains!
The straight part
We know that "Grinder" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case grinder = premolar.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PREMOLAR mean?
PREMOLAR noun- A tooth situated in front of the molar teeth; especially a tooth in humans with two cusps which is between the canines and the molars (Latin: singular dens premolaris, plural dentes premolares)
- Before a molar tooth, either in physical position or in its time of development; deciduous.