noun
single track; single line
Refers to a railway line with a single set of tracks, where trains in both directions share the same track.
この路線は単線なので、すれ違いに時間がかかる。
This line is single-track, so passing each other takes time.
noun
solid wire; solid-core wire; single-strand wire
Used in electrical contexts to describe a wire consisting of a single solid conductor, as opposed to stranded wire.
Solid wire is harder to bend than stranded wire, but connections are more secure.