ə̇nˈgreshən noun
( -s )
Etymology: Middle English, from Latin ingression-, ingressio, from ingressus (past participle) + -ion-, -io -ion
1. : the action of entering : entrance
2. : the process whereby potentialities or eternal objects enter into or become complex actual occasions or events
the ingression of an object into an event is the way the character of the event shapes itself in virtue of the being of the object — A.N.Whitehead
3. : inward migration in gastrulation of large yolk-laden macromeres formed by holoblastic but markedly unequal cleavage