window envelope

English Thesaurus

1. an envelope with a transparent panel that reveals the address on the enclosure (noun.artifact)

hypernym	:	envelope,
definition	:	a flat (usually rectangular) container for a letter, thin package, etc. (noun.artifact)

part holonym	:	window,
definition	:	a transparent panel (as of an envelope) inserted in an otherwise opaque material (noun.artifact)