What is the word for the relationship between two angles that add up to 360˚ If A+B = 180˚ they are supplementary to each other but what would you call their relationship if they add up to 360˚?
 A: One term that has been used is "Explementary". For example, see this: http://www.pballew.net/arithme6.html#explemen 
However, I would consider this sufficiently obscure that you should avoid using it without (re)defining it. And if you just need to use the concept once or twice, just say what you mean rather than using that term.
(Another term (same reference) appears to be "conjugate", but since that already has very well established alternative meanings, it can cause even more confusion).
A: Just as Deepack said they are called explementary angles and those that add to less than 360 degrees are reflex angles remember for future reference. 
A: The symmetrical word to use is "explementary" but - as above - is seldom or never used. Since terminology and language in general is intended to convey meaning, it's relatively useless when so few people use/know it.
Another way to phrase the pairing is to say that the larger is the reflex angle of the smaller (so 210 degrees is the reflex angle of 150 degrees). In most notations, the presumption is that an angle ABC will be the interior (that is, measuring up to 180 degrees) angle between rays BA and BC. If you intend the exterior angle, you would speak about the reflex angle ABC. Thus the larger angle is the reflex of the smaller angle, and they must necessarily sum to 360.
