Word for opposite parallel vectors

Given two points, A and B, there are two vectors: A-->B and A<--B which are parallel but pointing in opposite directions. I remember learning as a kid a word which simply defines the line upon which the vectors lie and another which defines the direction the vectors move along the line, something like "A-->B and A<--B have the same XXX, but opposite YYY." Can anyone fill in these blanks?

• All I can find is "opposite vector" or "negative vector". Is it something other than that? Jun 29, 2015 at 19:59
• I expect you would get an answer quicker on math.stackexchange.com
– Avon
Jun 29, 2015 at 20:00
• @Catija No, I distinctly remember the structure being as given: "A-->B and A<--B have the same XXX, but opposite YYY". Jun 29, 2015 at 20:01
• Opposite sense. Jun 29, 2015 at 20:10
• Your title doesn't clearly reflect the content of the body, and I think my answer reflects the title more than the body. Is my answer appropriate, or should I delete it? Jun 29, 2015 at 20:44

same magnitude and opposite direction

The vectors are called antiparallel:

In a Euclidean space, two directed line segments, often called vectors in applied mathematics, are antiparallel, if they are supported by parallel lines and have opposite directions.

Note: Two antiparallel vectors need not have the same magnitude (i.e. length); they can be of any length.

same axis but opposite direction?

• Axis? For a vector? Never heard that used in this context.
– Drew
Jun 29, 2015 at 20:37