Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
jējūno, 1, v. n. [com. ], to fast (late Lat.): Abraham peregrinis prandentibus cibos jejunaturus apposuit, Hier. Ep. 66, 11: cum jejunas laeta sit facies tibi, id. ib. 22, 27.