Number moving south with a need, disheartened (8)
I believe the answer is:
thousand
'number' is the definition.
(thousand is a kind of number)
'moving south with a need disheartened' is the wordplay.
'moving' indicates an anagram.
'with' is a charade indicator (letters next to each other).
'disheartened' means to remove the middle letters.
'need' with its centre removed is 'nd'.
'south' is an anagram of 'thous'.
'thous'+'a'+'nd'='THOUSAND'
(Other definitions for thousand that I've seen before include "Roman numeral M" , "Ten hundreds" , "Ten hundred" , "Numeric value of kilo" , "-- Island dressing" .)