lancet vs lancet arch

lancet and lancet arch both are nouns.

Word	Noun	Adjective	Verb	Adverb
lancet	Yes	No	No	No
lancet arch	Yes	No	No	No

As nouns, lancet and lancet arch are synonyms defined as:

lancet (noun)	lancet arch (noun)
a surgical knife with a pointed double-edged blade; used for punctures and small incisions	an acutely pointed Gothic arch, like a lance
an acutely pointed Gothic arch, like a lance