Magus III

From Memory Alpha, the free Star Trek reference.

You may be looking for Makus III.

Magus III is a planet that has been visited by Guinan.

In 2367, when REM sleep-deprived crewmembers aboard the USS Enterprise-D began to draft conspiracy theories about their inability to escape the Tyken's Rift in Ten Forward, Guinan was able to defuse the situation by firing an energy-beam rifle at the ceiling. She said she had acquired the weapon on Magus III. (TNG: "Night Terrors")