Close thought with money helping to support criminal (13)
I believe the answer is:
concentration
'close thought' is the definition.
(concentration is thinking hard about something)
'money helping to support criminal' is the wordplay.
'money' becomes 'cent' (eg denomination of dollars).
'helping' becomes 'ration' (a ration is a serving or helping).
'to support' means one lot of letters go next to another (in a down clue, some letters hold up others).
'criminal' becomes 'con' (abbreviation for 'convict').
'cent'+'ration'='centration'
'centration' after 'con' is 'CONCENTRATION'.
'with' is the link.
(Other definitions for concentration that I've seen before include "Focussing" , "Deep thought" , "Complete attentiveness" , "stronger solution" , "A close gathering of things" .)