Having a flat or flattened upper surface(adjective)
WordNet. Princeton University. 2010.
Use "flat-topped" in a sentence
"His son, Sarbjeet Singh, who sports a flat-topped hairdo says only two of his friends have gotten jobs outside of farming—and they had to leave the country to find them."
"It is here you will find the distinctive blue canopy of Neal's Yard Dairy with its flat-topped pyramids of Tymsboro cheese."
"All classics with the astounding performance by Boris Karloff in the 1931 Frankenstein showing why the flat-topped creature is one of cinema's defining images."