Speculation, wearing robe (10)
I believe the answer is:
investment
'speculation' is the definition.
(I've seen this in another clue)
'wearing robe' is the wordplay.
'wearing' becomes 'in' (you are 'in' the clothes you're wearing).
'robe' becomes 'vestment' (vestment is a kind of robe).
'in'+'vestment'='INVESTMENT'
(Other definitions for investment that I've seen before include "Something bought for its future value" , "Something intended to yield profit" , "One way to make gains" , "Profitable asset" , "speculation" .)