Wow, this is the one thing I know about in biology 

A dicotyledon plant is broad, and have a 'network' of veins. 

 <-- this is a picture of one so you know what I mean.
A monocotyledon is the opposite. They are long and narrow, with very straight veins. The veins are parallel. 

 <-- There is a picture of one so you know what that looks like too.
Hope this helps, and that you manage to see it 
