springer vs impost

springer and impost both are nouns.

Word	Noun	Adjective	Verb	Adverb
springer	Yes	No	No	No
impost	Yes	No	No	No

As nouns, springer and impost are synonyms defined as:

springer and impost: the lowest stone in an arch -- from which it springs

springer (noun)	impost (noun)
a cow about to give birth	the lowest stone in an arch -- from which it springs
a large spaniel with wavy silky coat usually black or liver and white	money collected under a tariff
the lowest stone in an arch -- from which it springs