perpendicular – (adjective) at a right angle with (90 degrees)
perpendicularly – (adverb) being at a right angle with (90 degrees)
The roof is perpendicular to the two columns.
Those two lines aren’t perpendicular, they’re parallel to each other.
The cars in the photo on the left-hand side are parked perpendicularly.
When the line of a fishing rod isn’t hanging perpendicularly, it may mean a fish is pulling at your bait.