If two vectors are parallel they are said to be collinear. In this case they can share the same direction or they can point to opposite directions. 1. For two parallel vectors sharing the same direction can I say that tey are codirected? Is it a true English word? I did not find it in A.J.Lohwater's Russian-English dictionary published by AMS. If it is not a true word, which adjective is suitable for denoting such a pair of vectors? 2. For two parallel vectors pointing to opposite directions which form is better to say: - they are opposite directed or opposite-directed; - they are contrary directed; - they are counter-directed or counterdirected? Please help me to choose a true wording.