Walter giving a hand to a Yankee (5)
I believe the answer is:
mitty
'walter' is the definition.
(main character in The Secret Life of Walter Mitty)
'giving a hand to a yankee' is the wordplay.
'giving' means one lot of letters go next to another.
'a hand' becomes 'mitt' (synonyms).
'to a yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'mitt' put next to 'y' is 'MITTY'.
(Other definitions for mitty that I've seen before include "Walter ---, Thurber's fantasist" , "Walter --, Thurber's daydreaming hero" .)