I'm trying to follow a recipe that calls for a pureed cucumber but I don't own a blender, how can I get the cucumber to a decent consistancy w/o one?

You could use a mortar and pestle to mash it. Or put into a Ziploc, mash with a rolling pin, and push through a colander.

A food mill, if you have one. If your knife skills are reasonably good you could chop it into submission in a short time. If this sort of thing comes up for you at all often, you might look into an immersion blender- they're quite cheap and take up very little room.

Agree with 2 methods suggested.
Another ,,, chop very finely, with a little salt added.
For all three methods, catch the cucumber liquid and - depending on the recipe, mix it in.

Mash it through a sieve after chopping or grating.

Try grating it on the large holes of a box grater....