having one color or shades of the same color
monochrome
an eyeglass for one eye
monocle
speaking or writing only one language
monolingual
something made out of one single large block or piece of stone; on single stone monument
monolith
a long speech given by one person
monologue
an abnormal fear of being the only one there; fear of being alone
monophobia
control of a product or service by one company
monopoly
a track for subway or train cars that only has one rail
monorail
having only one syllable
monosyllabic
a speech in which every word has one tone of voice
monotone