Capone and Eisenhower appear similar (5)
I believe the answer is:
alike
'similar' is the definition.
(synonyms)
'capone and eisenhower' is the wordplay.
'capone' becomes 'Al' (gangster Al Capone).
'and' says to put letters next to each other.
'eisenhower' becomes 'Ike' (Ike was a nickname of President Dwight Eisenhower).
'al'+'ike'='ALIKE'
'appear' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for alike that I've seen before include "Dull pain" , "Undistinguished" , "Comparable or similar" , "uniform" , "twins, perhaps" .)