They can sort out the costs (5)
I believe the answer is:
scots
'they can' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'sort out the costs' is the wordplay.
'sort out' indicates anagramming the letters.
'costs' is an anagram of 'SCOTS'.
Can you help me to learn more?
(Other definitions for scots that I've seen before include "People from north of border" , "eg Glaswegians" , "Glaswegians, Aberdonians etc" , "Northern language" , "North British" .)