unknownpurpose
nounUK /ʌnˈnəʊn ˈpɜːpəs/
US /ʌnˈnoʊn ˈpɜːrpəs/
A reason for doing something that nobody knows.
The box sat in the attic with an unknownpurpose for years.
OTHER MEANINGS
2. Something made without a clear use.
The strange gadget had an unknownpurpose.
3. A plan that is kept secret from everyone.
The club met with an unknownpurpose.
4. A task whose reason is not explained.
He was given an unknownpurpose and told to wait.