I have heard different people use these terms differently. Some people say a test vector is a single test cycle, and a test pattern is a collection of test vectors, but I have heard others that use test pattern and test vector as if they were the same.
One a tester, you would see 'a vector number' in a test file, so I guess tester people will tell you that a test vector is a single test cycle.
When there is an ambiguity, I usually use 'single vector' or 'test vector set' instead of vector or pattern.