Possible Clues:

• Four-faced solid
• Solid with four triangular faces
• Hard to enter false figure
• Bending tree not hard, solid
• A regular ____ can be described as a triangular pyramid
• Solid with four faces
• Type of pyramid
• Few planes can contain this wild deer, not holding stag back
• What you'll draw in this grid if you 18-Across with six straight lines
• Four-sided figure