This is the 7022nd most frequent Dutch word.
andersom
"Opposite" or "the other way around."
In this sentence, 'andersom' means 'the other way around,' referring to the orientation of the key.
De sleutel past niet; hij moet andersom in het slot.
The key doesn't fit; it must be turned the other way around in the lock.
Here, 'andersom' expresses the idea of being 'the other way around,' referring to a mistaken perception being contrary to reality.
Ik dacht dat het andersom was, maar blijkbaar had ik het mis.
I thought it was the other way around, but apparently I was wrong.
In this use, 'andersom' implies 'laid with the reversed side or orientation,' discussing the arrangement of tiles in a renovation.