The most common and most likely answer to this crossword clue is the 8 letter word GNASHING
I've seen this crossword clue in The Guardian
G
N
A
S
H
I
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G
More clues leading to the result GNASHING
Buddy explains!
The straight part
We know that "making hard grind" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case making hard grind = gnashing.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 GNASHING mean?
GNASHING verb- To grind (one's teeth) in pain or in anger.
- To grind between the teeth.
- To run away.
- The action of something that is gnashed.