Roughly calculate one million is invested in property (8)
I believe the answer is:
estimate
'roughly calculate' is the definition.
(I've seen this before)
'one million is invested in property' is the wordplay.
'one million' becomes 'im' (resembles em).
'is invested in' indicates putting letters inside.
'property' becomes 'estate' (estate is a kind of property).
'im' placed within 'estate' is 'ESTIMATE'.
(Other definitions for estimate that I've seen before include "Make an approximate assessment" , "Make approximate judgement of size or amount" , "Make an educated guess" , "Statement giving the likely cost of a job" , "calculate aproximately" .)