Unstable, like some mountain peaks? (5)
I believe the answer is:
rocky
'unstable' is the definition.
(similar in meaning)
'like some mountain peaks?' is the wordplay.
I cannot really understand how this works, but
'like' could be 'y' (similar in meaning) and 'y' is present in the answer.
The remaining letters 'rock' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for rocky that I've seen before include "likely to collapse" , "Unsteady, unstable" , "Wobbling" , "lacking 15d [STABILITY]" , "'-' Marciano, US boxer" .)