Belly button (5)
'belly button' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for navel that I've seen before include "Tummy button" , "Variety of orange" , "Where the umbilical cord was once attached" , "Scar on the stomach (for gazing at?)" , "Something to contemplate" .)
(Other definitions for umbilicus that I've seen before include "Navel" , "Something in the tummy" .)