An artist took one in (5)
I believe the answer is:
monet
'an artist' is the definition.
(I've seen this before)
'took one in' is the wordplay.
'took' becomes 'mt' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'mt' going around 'one' is 'MONET'.
Can you help me to learn more?
(Other definitions for monet that I've seen before include "Claude ---, painter (waterlilies)" , "French Impressionist with famous garden" , "Claude --, French impressionist painter" , "Claude -, French artist" , "Claude, impressionist painter, d. 1926" .)