Male elected to keep investment, in error (8)
I believe the answer is:
mistaken
'in error' is the definition.
'male elected to keep investment' is the wordplay.
'male' becomes 'm' (common abbreviation).
'elected' becomes 'in'.
'to keep' means one lot of letters goes inside another.
'investment' becomes 'stake' (stake is a kind of investment**).
'in' enclosing 'stake' is 'istaken'.
'm'+'istaken'='MISTAKEN'
(Other definitions for mistaken that I've seen before include "Wrong (in judgement)" , "Wrong-headed" , "In error in mankiest way" , "Wrong in opinion, judgment etc." , "Erroneous" .)