From WordNet (r) 3.0 (2006) [wn]:
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"
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]