せんにゅう潜入sennyuu
1.
The act of secretly entering a place without being detected, often for purposes of surveillance or espionage.
2.
A hidden or stealthy approach into an area, typically associated with covert operations or clandestine activities.
Example:
彼は農夫に身をやつして城下町に潜入した。
せんにゅうしゃ潜入者sennyuusha
1.
A person who secretly enters a place or organization with the intention of gathering information or causing disruption.
2.
Someone who embeds themselves covertly within a group or system to observe or operate without detection.
3.
An individual who crosses boundaries, often in a stealthy manner, to gain access to restricted areas for a specific purpose.