Forsythe

This surname has two possible origins. The more accepted explanation is that it comes from the Gaelic given name Fearsithe, which means "man of peace" from the elements fear "man" and sithe "peace". The less accepted explanation is that it originated as a habitational name for a person from some minor or lost place called Fersith or Forsith, which is suggested by some early forms with prepositions (for example, de Fersith, recorded in 1365). The hypothetical place name perhaps meant "fairy pastures" or "fairy mound" from the Gaelic elements fer "grass" or for "hill, mound" and sithe "fairies"; however, no place name of suitable form is known.

This spelling is associated chiefly with northern Ireland.