Oddly, niece to dress outside in necessities (5)
I believe the answer is:
needs
'necessities' is the definition.
(I know this)
'oddly niece to dress outside' is the wordplay.
'oddly' indicates alternate letters (letters in odd-numbered positions).
'to' is a charade indicator (letters next to each other).
'outside' suggests removing the centre.
'dress' with its middle taken out is 'ds'.
The alternating letters of 'niece' are 'nee'.
'nee'+'ds'='NEEDS'
'in' acts as a link.
(Other definitions for needs that I've seen before include "Necessities" , "Things that are wanted" , "Requirements" , "Requires or lacks" , "Is desperate for" .)