Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
bētācĕus, a, um, adj. [1. beta], from or of the beet: pedes betacei, beet-roots, Varr. R. R. 1, 2, 27.
Subst.: bētācĕus, i, m. (sc. pes), beet-root (cf. Charis. pp. 24 and 128 P.; Prisc. p. 618 ib.), Apic. 3, 2; Plin. Ep. 1, 15, 2 (where others, less correctly, read Baeticae); Arn. 4, p. 133 (others, betis).