Found in a stable environment or unstable terrain? (7)

I believe the answer is:

trainer

I'm a little stuck... Click here to teach me more about this clue!

'found in a stable environment' is the definition.
I can't tell whether this definition defines the answer.

'unstable terrain?' is the wordplay.
'unstable' indicates an anagram.
'terrain' with letters rearranged gives 'TRAINER'.

'or' is the link.

Can you help me to learn more?

(Other definitions for trainer that I've seen before include "Sports footwear" , "Sports coach" , "Casual 11 ac" , "Coach - item of footwear" , "Shoe; educator" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

Want a hint initially instead of a full solution? Install my app