Source : Webster's Revised Unabridged Dictionary (1913)

-er \-er\
   .

   1. [AS. -ere; akin to L. -arius.] The termination of many
      English words, denoting the agent; -- applied either to
      men or things; as in hater, farmer, heater, grater. At the
      end of names of places, -er signifies a man of the place;
      as, Londoner, i. e., London man.

   2. [AS. -ra; akin to G. -er, Icel. -are, -re, Goth. -iza,
      -?za, L. -ior, Gr. ?, Skr. -[=i]yas.] A suffix used to
      form the comparative degree of adjectives and adverbs; as,
      warmer, sooner, lat(e)er, earl(y)ier.