How about a cone or a pyramid
Cone
A cone has a round base and a narrowing round top. I hope this answers your question!
pyramid or cone
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How about a cone or a pyramid
a pyramid
A 3D shape with one base and three faces can only have triangular faces.
Pyramid
Cone
A polygonal pyramid.
a polygonal prism or a polygond
triangular prism
The sphere.
A cone, possibly.
How about a hemisphere ?
A pyramid is a solid figure with one vertix.