Expansive is all about being able to grow or get larger. An expansive piece of land is large, an expansive mind is one that is always thinking of the big picture, an expansive vocabulary is one that holds lots of words.
Warning: don't confuse expansive, "large," with expensive, "high priced." They differ by only one letter but mean very different things. A Big Mac may contain what McDonald's advertizes as an expansive all-beef patty, but it isn't expensive food.
adj able or tending to expand or characterized by expansion
capable of being distended; able to stretch and expand
filled with vascular sinuses and capable of becoming distended and rigid as the result of being filled with blood
expandable, expandible, expansible
able to expand or be expanded
designed to be filled with air or gas
showing no tendency to expand