Which term is synonymous with the act of entering into?

The term that is synonymous with the act of entering into is "incursion." This word typically describes the act of entering a place, often implying some form of intrusion or invasion. In various contexts, it can refer to a military entry into a territory or a less aggressive form of entering an area for exploration or research. Its meaning encapsulates the essence of entering something, making it closely aligned with the question's requirement.

In contrast, the other terms have distinct meanings that do not resonate with the idea of entering. "Segregation" refers to the separation of groups, often based on social or demographic factors, and does not imply entry into a space. "Incitement" suggests the act of provoking or urging someone to act, typically in a context that incites unrest or action, which is unrelated to the notion of entering. "Infiltration," while it involves entering, specifically connotes a secret or stealthy entry, often for nefarious purposes, which can differ significantly from the general act of entering.