Height affects an ordinal number below the tenth (6)
I believe the answer is:
eighth
'an ordinal number below the tenth' is the definition.
I can't tell whether this defines the answer.
'height affects' is the wordplay.
'affects' indicates anagramming the letters (I've seen 'affected' mean this).
'height' anagrammed gives 'EIGHTH'.
Can you help me to learn more?
(Other definitions for eighth that I've seen before include "One after seventh" , "Arm muscle" , "12.5 per cent" , "The latest Henry or Edward?" , "Half a quarter" .)