Duke and stranger to move unsteadily (6)
I believe the answer is:
dodder
'move unsteadily' is the definition.
(I've seen this in another clue)
'duke and stranger' is the wordplay.
'duke' becomes 'd' (abbreviation).
'and' means one lot of letters go next to another.
'stranger' becomes 'odder' (I've seen this before).
'd'+'odder'='DODDER'
'to' acts as a link.
(Other definitions for dodder that I've seen before include "Totter into the Dublin river" , "Move in frail manner" , "Hesitate" , "Be decrepit in the Dublin river" , "Progress unsteadily (due to age?)" .)