Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† archĕtypus, a, um, adj., = ἀρχέτυπος, that was first made, original (very rare): archetypos servare Cleanthas, i. e. the original statues of Cleanthes, Juv. 2, 7. So Martial calls the original MSS. of his epigrams, archetypae nugae, 7, 11, and in jest, friends that cost nothing, archetypi amici, 12, 69.
Hence, subst.: archĕty-pum, i, n., an original, Varr. R. R. 3, 5, 8; so Plin. Ep. 5, 10; Macr. S. 7, 14.