The most common and most likely answer to this crossword clue is the 8 letter word QUAVERED
Q
U
A
V
E
R
E
D
Buddy explains!
The straight part
We know that "was on shaky grounds" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case was on shaky grounds = quavered.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.
Crossword Answer definitions
QUAVERED verb- To shake in a trembling manner.
- To use the voice in a trembling manner, as in speaking or singing.
- To utter quaveringly.