Visitor to Siam (4)
I believe the answer is:
anna
'visitor to siam' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for anna that I've seen before include "Former Indian coin; girl's name" , "Miss Karenina" , "was of very small account in India" , "- - and the King of 22" , "Dame -- Neagle" .)