Crusty old American on container ship? (12)
I believe the answer is:
cantankerous
'crusty' is the definition.
(thesaurus)
'old american on container ship?' is the wordplay.
'old american' becomes 'ous' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters go next to another.
'container' becomes 'can' (can is a kind of container).
'ship?' becomes 'tanker' (ship carrying liquids).
'can'+'tanker'='cantanker'
'ous' put after 'cantanker' is 'CANTANKEROUS'.
(Other definitions for cantankerous that I've seen before include "Difficult" , "Stubbornly obstructive" , "Grumpy" , "Cross" , "can be prickly, too!" .)