Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
fu, interj., v. fue.
fue or fu (or fūfae, acc. to Charis. p. 213 P.), interj., denoting aversion, foh! fie! fu! Plaut. Most. 1, 1, 37; id. Ps. 5, 2, 5.
2. phu or fu, interj., foh! fugh! phu in malam crucem, Plaut. Ps. 5, 2, 5 (Ritschl, fu); cf. Charis. p. 213 P.; Prisc. p. 1024 ib.