Unhyphenated

The word cooperation is unhyphenated, though some also spell it as co-operation.

Source: wiktionary

... when we shall recognize in our press and at the ballot box no votes but American votes, and no citizens but simply unhyphenated American citizens; when we shall insist that every man who places a ballot in our ballot box shall be able to read that ballot in the language of Lincoln and Grant, we shall have reached the hour when we may begin the most momentous and delicate task ever set before a people—the creation of a great nation out of the fragments of many diverse and even hostile nationalities.

Source: wiktionary

For Pennsylvania yields to no State in the courage and virility of her sons—plain, unhyphenated Americans, not yet pushed by invaders off the soil; loyal men, whose fathers gave their blood like water for the Union.

Source: wiktionary

First of all, and probably greatest of all in view of most present-day writers, they were "unhyphenated!" This is indeed wonderful! And again, most wonderful! Unhyphenated! So interesting a fact as this, and one so eminently desirable, invites most critical investigation, for the very breath of suggestion insinuates at once that "hyphenism" and "Americanism" are by the very nature of things contradictory, and that "hyphenism" must needs be on a par with, if not exactly the same as, treason. We are therefore very much interested in the new fact that Pennsylvania's glory lies in the giving of "unhyphenated" Americans to the new nation born of the travails of the Revolution.

Source: wiktionary