from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Infiltration of the genes of one species into the gene pool of another through repeated backcrossing of an interspecific hybrid with one of its parents.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The movement of a gene from one species to another
from the GNU version of the Collaborative International Dictionary of English
- n. The act of going in; entrance.
from The Century Dictionary and Cyclopedia
- n. The act of going in or of proceeding inward; entrance.
From Latin intrōgressus, past participle of intrōgredī, to step in : intrō-, intro- + gradī, to step; see ghredh- in Indo-European roots.(American Heritage® Dictionary of the English Language, Fourth Edition)
introgress + -ion (Wiktionary)