TL;DR: You can mount this lens on a Nikon DSLR only with a "speedbooster" lens adapter.
seller says fits canon 49mm. won't fit my camera since I have nikon D5500 which I think is 52mm
The "⌀49mm" means the lens takes 49mm filters (the circle with the line through it is the diameter symbol).
I'm not sure what the seller refers to by "Canon 49mm" (or by Nikon 52mm). However, if the lens is a Canon mount, it is probably a Canon FD mount (which was made obsolete by the Canon EF mount when they introduced their EOS cameras).
Assuming the lens is made for a Canon mount, it will not mount on a Nikon body without a "speedbooster" adapter. This is because the registration distance (also sometimes known as flange focal distance, such as at Wikipedia) of Canon's FD mount FFD is 42.0mm, and Nikon's F-mount FFD is 46.5mm. This means that compared to the Canon FD body, a Nikon body is 4.5mm too thick. And a bayonet mount adapter will add even more distance between the body and lens. If you mount a lens too far away from the sensor/film plane, you lose the ability to focus on distant subjects.
If you wanted to mount this lens to a Nikon F-mount DSLR (again, assuming this one is made for Canon mount), you'd need a so-called "speedbooster" (it's a mount adapter that has a refocusing element in it, to allow the Vivitar lens to focus to infinity when mounted further from the body than the designed FFD). For example, Fotodiox sells such an adapter for around $35 USD.
Related questions for further reading and explanation:
Is Vivitar 28mm 1:2.8 lens a good lens, and what kind of things can I use it for?
This is considered wide angle lens when mounted on a full-frame body; On your D5500, this is considered a more-or-less normal focal length / field of view (having the same angle of view as a 35mm lens mounted on a full frame body).
For its price, it's apparently a decent little lens:
However, because you need to add a corrective lens element (the speedbooster) when mounted on Nikon bodies, the optical quality will likely be somewhat reduced. You can minimize this loss of optical performance by using a higher quality speedbooster. However, there are not very many options on the market for Canon FD lens to Nikon F-mount body adapters. The adapters will probably cost more than the lens.
In general, as a Nikon body owner, you will have to get used to having fewer lens choices (as far as adapting other brand lenses to Nikon) than any other mainstream market camera brand. Unfortunately, that's just part of the Nikon system experience.
Note: I originally assumed this lens was a Minolta MC/MD mount lens because of the "MC" text on the lens; as @osullic helpfully pointed out, "MC" stands for Multi-coated, meaning the lens has a multi-coat antireflective coating on at least one of the lens elements to prevent glare and lens reflections.