Failure initially in stability device (3)
I believe the answer is:
fin
'stability device' is the definition.
'fin' can be an answer for 'device' (fin is a kind of device). I am not sure about the 'stability' bit.
'failure initially in' is the wordplay.
'initially' says to take the initial letters.
The first letter of 'failure' is 'f'.
'f'+'in'='FIN'
Can you help me to learn more?
(Other definitions for fin that I've seen before include "Fishy appendage" , "Thin projection for fish to steer itself" , "Piscine appendage" , "For movement and balance in fish" , "Paddle-like organ" .)