Act the part of in public, usually alluding to a performance on stage. For example, She got wonderful reviews when she appeared as Portia. This idiom uses appear in the sense of “to come before the public,” a usage dating from the late 1500s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.