In kindergarten, a dirty bottom (5)

I believe the answer is:
nadir
'bottom' is the definition.
(I've seen this in another clue)
'in kindergarten a dirty' is the wordplay.
'in' indicates the answer is hidden within the clue.
'NADIR' can be found hidden inside 'kindergarten a dirty'.
(Other definitions for nadir that I've seen before include "most unsuccessful point" , "Drain to lowest level" , "Drain into the lowest point (5)" , "pits" , "Point of greatest despair" .)