Walk furtively (up to someone) (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
sidle
(Other definitions for sidle that I've seen before include "Move in furtive or timid manner" , "Slide (anag.)" , "Make cautious progress" , "Edge along furtively" , "Isled (anag.)" .)