Synonyms of er

1 Syllable
oops, rah, pooh, hey, oop, ugh, ah, wow, um, boo, ouch, ums, huh, shucks, phew, phooey, psst, oh
2 Syllables
hooray, oh's, hello, hurrah, amen, egad, whoopee, icu, ahem, golly, alas, jeepers
4 Syllables
interjections, interjection, exclamation