A monocot has only one seed leaf (monocot is short for 'monocotyledon'. A cotyledon is a seed leaf, and 'mono' means one). This seed leaf is usually the same shape as the adult leaf, long and thin, and the leaf veins nearly always run parallel to the central midrib.
Dinocot or Dicot???
If A dicot has two cotyledons (dicot is short for 'dicotyledon', and 'di' means two). The seed leaves are usually rounded and fat, because they are the two halves of the seed. The first true leaves can be many different shapes, from long and thin to rounded or palmate. Most trees and shrubs and many garden annuals and perennials are dicots, and there are many more species of dicots than there are monocots.