transitive verb

1. to spread out; open out; stretch out; unfold the eagle expanded its wings
2. to make greater in size, bulk, scope, etc.; enlarge; dilate; extend
3. to enlarge upon (a topic, idea, etc.); develop in detail
4. to work out or show the full form of (a contraction, mathematical equation, etc.)

Etymology: ME expanden < L expandere < ex-, out + pandere, to spread, extend; akin to patere: see fathom

intransitive verb

1. to become expanded; spread out, unfold, enlarge, etc.
2. to become affable, warmly communicative, etc.