Yes, negative is a noun there, and 'neg' is short for negative. Film used to come on reels, and the cutter would cut the film, like a precision pair of scissors. The cut would be aligned to the holes and between the images. You could then splice two cut ends together. In the photographic process, silver turns dark when it gets light on it. So, in a camera, light areas in a scene become dark areas on the film, and hence are a 'negative' of the original image. If you then shine light through the negative onto another film, to make a copy, the dark areas on the film block the light, and the new film doesn't go dark. This is then a 'positive'. If you shine light through a positive, you get an image that is the same as the original scene. Make sense?

This is a technical term used in photography and film and has to do with an image on a plastic film.

A guy who cut the first film. He/she's a cutter of negatives, so "neg" is an adjective on the person/people. Celluloid film, as in real "film", the original, used to be a process that produced a negative image on the first use. For a black and white photo, this means that dark areas of the scene are light on the negative and light areas are dark. Light areas of the negative are clear. Dark areas are dark, not letting light through. The next process was to print this film onto paper which was the photo that you would get to look at. This process shone a light throught the neagtive, so any areas of the negative that were clear let light through and exposed the photgraphic paper, which reacted by turning dark. This making it dark as the same area of the original scene. A lab that developed for you would develop the negatives and print to paper, any positives that you wanted. Any time you wanted, you could get more prints (positives) printed from the negatives. For colour photos a similar thing happens, the negative has each of the colours inverted, light for dark, so when light shines through it it looks negatie, inverted. This light exposed photgraphic paper that darkened in that colour when exposed to light, making it back to the colour of the original scene.