'rank-and-file' is an English compound formed from 'rank' and 'file', where 'rank' originally meant 'a line or row' and 'file' meant 'a line or column' (with 'file' ultimately from Latin 'filum' meaning 'thread').

'rank-and-file' developed from military usage (phrases like 'ranks and files') in early modern English to describe the lines of soldiers; it was later applied metaphorically to the ordinary members of any organization.

Initially it referred to literal lines of soldiers ('rows and columns'); over time it evolved to mean the ordinary members of an organization as opposed to its leaders.