Relating to the region between the Earth and the Moon, or occurring in space within that zone.
From Latin 'cis-' (on this side of) combined with 'lunar' (relating to the Moon). This aerospace term developed in the 20th century as space exploration made such spatial distinctions meaningful.
NASA uses this term constantly when talking about space missions—it's the 'suburb' of space between us and the Moon, and it's about to get incredibly busy with new moon bases and cargo missions in the next decade.
Complete word intelligence in one call. Free tier — 50 lookups/day.