Square number (4)
'square number' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nine that I've seen before include "Number IX" , "dancing ladies?" , "Number of Muses and days in a Novena" , "It's dialled three times in an emergency" , "One's married partner" .)
'square number' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sixteen that I've seen before include "Year for which 6 is remembered historically" , "8 x 2" , "Four squared" , "XVI" , "Sweet Little -, (Chuck Berry)" .)