The Collaborative International Dictionary of English v.0.48:

Immigration \Im"mi*gra"tion\, n. [Cf. F. immigration.]
   The act of immigrating; the passing or coming into a country
   for the purpose of permanent residence.
   [1913 Webster]

         The immigrations of the Arabians into Europe. --T.
                                                  Warton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

immigration
    n 1: migration into a place (especially migration to a country
         of which you are not a native in order to settle there)
         [syn: immigration, in-migration]
    2: the body of immigrants arriving during a specified interval;
       "the increased immigration strengthened the colony"

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

IMMIGRATION. The removing into one place from another. It differs from
emigration, which is the moving from one place into another. Vide
Emigration.