open sandwich vs open-face sandwich

open sandwich and open-face sandwich both are nouns.

Word	Noun	Adjective	Verb	Adverb
open sandwich	Yes	No	No	No
open-face sandwich	Yes	No	No	No

As nouns, open sandwich and open-face sandwich are synonyms defined as:

open sandwich and open-face sandwich: sandwich without a covering slice of bread

open sandwich (noun)	open-face sandwich (noun)
sandwich without a covering slice of bread	sandwich without a covering slice of bread