Strong men entering Spanish city with American (8)
I believe the answer is:
vigorous
'strong' is the definition.
('vigorous' can be a synonym of 'strong')
'men entering spanish city with american' is the wordplay.
'men' becomes 'or' (I've seen this in other clues**).
'entering' indicates putting letters inside.
'spanish city' becomes 'vigo' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'american' becomes 'us'.
'or' inserted into 'vigo' is 'vigoro'.
'vigoro'+'us'='VIGOROUS'
(Other definitions for vigorous that I've seen before include "energetic,strenuous" , "Strong, healthy" , "Strong and energetic" , "Full of energy and strength" , "Powerful, energetic" .)