Can half of us reverse a single thing? (4)
I believe the answer is:
unit
'a single thing?' is the definition.
(I've seen this in another clue)
'can half of us reverse' is the wordplay.
'can' becomes 'tin' (both are metal containers).
'half of' means to take half the letters.
'reverse' shows that the letters should be reversed in order.
'us' halved is 'u'.
'tin'+'u'='tinu'
'tinu' back-to-front is 'UNIT'.
(Other definitions for unit that I've seen before include "Item combining separate parts" , "Single item; one" , "Group that's part of a larger organisation" , "squad" , "Individual thing, single and complete" .)