This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 镹 is uncertain. It visually combines 镸 (long) and 久 (long time), but whether this is a semantic compound or a later formation is unclear.
The left side 镸 suggests length, and the right side 久 suggests a long time. Together they might evoke something enduring, but without a clear meaning, treat it as a shape to recognize.
For キュウ, imagine a long (镸) queue (久) of people waiting for a very long time: queue -> キュウ, and the long wait ties to the shape.