A first number in temporary accommodation were boarders (7)
I believe the answer is:
tenants
'boarders' is the definition.
(I've seen this in another clue)
'a first number in temporary accommodation were' is the wordplay.
'first number' becomes 'n' (sst letter of 'number').
'in' means one lot of letters goes inside another.
'temporary accommodation' becomes 'tent' (I've seen this before).
'were' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'a'+'n'='an'
'an' put into 'tent' is 'tenant'.
'tenant'+'s'='TENANTS'
Can you help me to learn more?
(Other definitions for tenants that I've seen before include "residents" , "Occupiers" , "They pay rent" , "Lodgers" .)