An allowance no single sailor rejected (6)
I believe the answer is:
ration
'an allowance' is the definition.
(I've seen this before)
'no single sailor rejected' is the wordplay.
'single' becomes 'I' (one).
'sailor' becomes 'tar' (slang term for a sailor).
'rejected' says the letters should be written in reverse.
'no'+'i'+'tar'='noitar'
'noitar' in reverse letter order is 'RATION'.
(Other definitions for ration that I've seen before include "Fixed allotment" , "Apportion" , "A measured portion in times of scarcity" , "Portion, share" , "Share or allotment, of food say" .)