W = Wide, SW = Super Wide. Do note that focal length is a bad predictor of covering angle, a 120 mm might be superwide on its intended format (8x10").
M = (medium image circle, meaning the lens will only provide moderate amounts of movements on the camera). This allowed for very small, light-weight lenses.
Nikon also had the AM series for close-ups, of these the most known is the 120 mm f/5.6 AM Nikkor ED (for 4x5" and smaller) , another was the 210 mm f/5.6 AM ED. These lenses are optimised for 1:1 (life-size) and the maker claims they keep the quality in the range 5:1 to 1:5. In practice, even to infinity if you have a suitable camera but then the image circle is severely constrained.
The most exciting large-format Nikkor series was the T ED range, starting at 270/6.3 T ED and going all the way up to 1200 mm f/18 T ED. They came in two subseries, 360-500-720 and 800-1200 focal lengths. Within each series you changed focal length by replacing the entire rear part of the lens with a dedicated lens component, not unlike a TC today. No such adaptation was offered for the 270 mm though. A pity as this probably was one of very best performing LF Nikkors. I used the 270, 360, 500, and 720 versions and still possess most of them (no longer the 720 today).
