Private lines (5)
I believe the answer is:
ranks
'lines' is the definition.
(I know this)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for ranks that I've seen before include "Lines or rows of people or things" , "Positions of seniority" , "Grades, in armed forces say" , "Classifies" , "Series of soldiers" .)