I think the proper term for something like '行き' would be the 'verb stem'...at least that's how I've always referred to it. And if you would, please, give us a sentence with an example? It would help.
Well, when using just the ます-stem (the expression used in Japanese For Busy People) without anything after it, the verb has magically changed into a noun! I think. So 行き would be "Going" or something like that
Usually you don't see this unless the stem-verb has something else in front of it making it a compound word. e.g 犬掻き (dog paddle), アメリカ行き (going to America) etc.