Sheepish climber gets oxygen first (5)
I believe the answer is:
ovine
'sheepish' is the definition.
(I've seen this before)
'climber gets oxygen first' is the wordplay.
'climber' becomes 'vine' (climbing plant).
'gets oxygen' becomes 'o' (I can't explain this - if you can you should give a lot more credence to this answer).
'first' is a charade indicator (letters next to each other).
'vine' put after 'o' is 'OVINE'.
Can you help me to learn more?
(Other definitions for ovine that I've seen before include "Like the Cheviots" , "Relating to sheep" , "Resembling a sheep" , "Pertaining to sheep" , "like a mug" .)