er

American Heritage® Dictionary of the English Language, Fourth Edition

1. interj. Used to express hesitation or uncertainty.

Century Dictionary and Cyclopedia

1. A Middle English form of ere.
2. An English suffix, originally and properly attached to verbs to form nouns of the agent, as in baker, creeper, delver, driver, reader, sower, writer, etc. Though denoting usually a person, it may denote also, or only, a thing, as ruler, heater, grater, poker, etc. In use it is equivalent to the Latin -or in such forms as instructor, one who instructs, actor, one who acts, confessor, one who confesses, etc. Accordingly, English verbs from Latin supine or perfect participle stems may form their noun of the agent with English -er or Latin -or: instructer or instructor, confesser or confessor, etc. Usually they prefer the Latin form, taking it directly (or mediately through Middle English -our, ⟨ Old French -our, ⟨ Latin -or, etc.) from the Latin, or forming it by analogy (as depositor, radiator, etc., for which there is no Latin original). The suffix -or is thus a rough means of distinguishing words of Latin origin: compare auditor, instructor, factor, etc., with their literal English equivalents hearer, teacher, doer, etc. In many words, as biographer, geographer, philologer, philosopher, etc., there is no accompanying verb, the suffix, which is equally referable to -er, being attached, cumulatively (first in philosopher), to the original (Latin or Greek) term signifying an agent. (See -er.) In another use, also without reference to a verb, -er, attached to names of towns or countries, signifies an inhabitant of or one who belongs to the town or country, as Londoner, New-Yorker, Hollander, Englander, New-Englander, etc., like German Berliner, Leipziger, Englander, Hollander, etc.
3. A suffix of Latin origin, denoting usually a person, and often an agent, but not, like -er, usually associated with a verb. It appears in justicer, commissioner, officer, prisoner, pensioner, etc. In many words of more recent formation the suffix may be taken as either -er or -er. In some words, as chancellor, it has assumed the form of Latin -or. In words recently formed or taken from the French it appears as -ier or -eer. In many words it has become merged or is mergeable with the English -er.
4. A suffix of adjectives, forming the comparative degree, as in colder, deeper, greater, bigger, etc., and being cognate with the Latin comparative suffix -or, -ior, neuter -us, -ius, represented in English in major, minor, minus, prior, superior, inferior, etc. In lesser, former, the suffix is cumulative. In better, worse, less (for irregular suffix, see etymology), the suffix is attached to a now non-existing positive. In upper, inner, outer, utter, etc., the positive is adverbial. See the words mentioned.
5. A suffix of verbs, giving them a frequentative and sometimes a diminutive sense, as patter from pat, swagger from swag, flutter from float, sputter from spout, etc. It is equivalent to and cognate with the frequentative -le (that is, -el), as in dialectal pattle = patter, scuttle from scud, etc. As a formative of new words it is scarcely used.
6. A suffix of certain nouns, mostly technical terms of the law (from Old Law French), as attainder, misnomer, trover, user, non-user, waiver, etc. In endeavor, endeavour, the orig. -er is disguised in the spelling.
7. In chem., the symbol for erbium.
8. In heraldry, an abbreviation of ermine.
9. A simplified spelling of err.

Wiktionary

1. interj. Said when hesitating in speech.
2. v. To utter the word "er" when hesitating in speech, found almost exclusively in the phrase um and er.

GNU Webster's 1913

1. n. the chemical symbol for erbium, a rare earth element. It has atomic number 68 and an atomic weight of 167.26.

WordNet 3.0

1. n. a trivalent metallic element of the rare earth group; occurs with yttrium
2. n. a room in a hospital or clinic staffed and equipped to provide emergency care to persons requiring immediate medical treatment