Dictionary, American, minimal cash invested – a tragedy (7)
I believe the answer is:
oedipus
'a tragedy' is the definition.
'dictionary american minimal cash invested' is the wordplay.
'dictionary' becomes 'OED' (Oxford English Dictionary).
'american' becomes 'us' (abbreviation for United States).
'minimal cash' becomes 'ip' (1 pence).
'invested' means one lot of letters goes inside another.
'oed'+'us'='oedus'
'oedus' enclosing 'ip' is 'OEDIPUS'.
(Other definitions for oedipus that I've seen before include "person who married his mother" , "Old Greek king who killed his father and married his mother" , "Complex man" , "who had parental problems" , "Mythical Greek king of Thebes" .)