WordWeb Online

1. To or at a greater extent or degree or a more advanced stage ('further' is used more often than 'farther' in this abstract sense)
   "the application of the law was extended farther"; "he is going no farther in his studies";
   - further
    
2. To or at a greater distance in time or space ('farther' is used more frequently than 'further' in this physical sense)
   "farther north"; "moved farther away"; "farther down the corridor"; "the practice may go back still farther to the Druids";
   - further

1. More distant in especially space or time
   "they live in the farther house"
    
2. More distant in especially degree
   "farther from the truth";
   - further

See also: far