I guess...
A Monorail is a singled-rail train system that runs in a direction
only.
The term "MONO" is like the sound system Stereo and Mono. Stereo
means 2 sides, in the case for here, 2 tracks. Mono means 1 side,
in the case for here, 1 track. Like wen you set the TV to Stereo
sound surround, two sides of the speaker is enabled, to Mono sound
system, only one side is enabled. In the case for here, a Monorail
is a train that runs on only one, one train track only. In the
cause for MRT, stereo.
Terms clarified.
Please, for goodness sake, stop arguing.