SHORT and SHORTENING
Shortening is an edible fat used to 'shorten' baked goods. Shortenings include lard (about 98% fat), butter (about 80% fat), margarine (about 80% fat) and processed shortenings made from vegetable oils, treated to produce an odorless, white shortening that is 100% fat - such as Crisco.
Because Crisco and similar flavorless shortenings were originally developed in the U.S., they are more well know here - and because they are 100% fat, they make the best shortening (leaving out the consideration of flavor that butter or lard give).
The term 'short'* has a very old derivation - it originally referred to substances that were easily crumbled, including coal, paper, dried dung, chalk, sand, etc. This most likely was based on the observation that friable (brittle, easily crumbled) substances had short fibers, or that they crumbled into shorter (smaller) pieces. The culinary use of 'short' dates back to at least the 15th century.
*(To make something shorter, means to cut into smaller pieces - see the connection?)
Short pastry has a high proportion of fat to flour, which produces a flaky dough - a dough which crumbles into shorter (smaller) pieces - (shortcake, short bread, short crust, etc).