Origin: 1400–50; late ME < L ingressus a going in, commencing, equiv. to ingred-, s. of ingredī to go or step into, commence (see in-2, gradient) + -tus suffix of v. action, with -dt- > -ss-
also in·gres·sion (ĭn-grěsh'ən) A going in or entering.
Right or permission to enter.
A means or place of entering.
[Middle English ingresse, from Latin ingressus, from past participle of ingredī, to enter : in-, in; see in-2 + gradī, to step; see ghredh- in Indo-European roots.]