Synonyms of 'perpendicular'
the perpendicular wall of sandstone
a narrow, exposed beach and perpendicular cliffs
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A precipitous slope or drop is very steep and often dangerous.
a steep, precipitous cliff
A sheer cliff or drop is extremely steep or completely vertical.
There was a sheer drop just outside my window.
Thesaurus for perpendicular from the Collins English Thesaurus
A perpendicular line or surface points straight up, rather than being sloping or horizontal.