The Collaborative International Dictionary of English v.0.48:

Filacer \Fil"a*cer\, n. [OE. filace a file, or thread, on which
   the records of the courts of justice were strung, F. filasse
   tow of flax or hemp, fr. L. filum thread.] (Eng. Law)
   A former officer in the English Court of Common Pleas; -- so
   called because he filed the writs on which he made out
   process. [Obs.] --Burrill.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

FILACER, FILAZIER, or FILZER, English law. An officer of the court of common
pleas, so called because he files those writs on which he makes out process.
FILE, practice. A thread, string, or wire, upon which writs and other
exhibits in courts and offices are fastened or filed. for the more safe
keeping and ready turning to the same. The papers put together in order, and
tied in bundles, are also called a file.
     2. A paper is said to be filed, when it is delivered to the proper
officer, and by him received to be kept on file. 13 Vin. Ab. 211.