unmanly adj.

prefix of negation, Old English un-, from Proto-Germanic *un- (source also of Old Saxon, Old Frisian, Old High German, German un-, Gothic un-, Dutch on-), from PIE *n- (source of Sanskrit a-, an- "not," Greek a-, an-, Old Irish an-, Latin in-), combining form of PIE root *ne- "not." Often euphemistic (such as untruth for "lie").

The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. It underwent a mass extinction in early Middle English, but emerged with renewed vigor 16c. to form compounds with native and imported words. It disputes with Latin-derived cognate in- (1) the right to form the negation of certain words (indigestable/undigestable, etc.), and though both might be deployed in cooperation to indicate shades of meaning (unfamous/infamous), typically they are not.

It also makes words from phrases (such as uncalled-for, c. 1600; undreamed-of, 1630s; uncome-at-able, 1690s; unputdownable, 1947, of a book; un-in-one-breath-utterable, Ben Jonson; etc., but the habit is not restricted to un-; such as put-up-able-with, 1812). As a prefix in telegramese to replace not and save the cost of a word, it is attested by 1936.

c. 1200, "human; characteristic of human beings," also "possessing virtues proper to a male person" (resoluteness, independence, steadfastness, reliability); from man (n.) + -ly (1). Meaning "masculine, not boyish or womanish, proper to fighting men" is attested from late 14c. Old English had werlic "male, masculine, manly."

Manly, matching womanly, is the word into which have been gathered the highest conceptions of what is noble in man or worthy of his manhood, especially as opposed to which is fawning or underhand. Manful expresses the stanchness, fearlessness, and energy of a man, as opposed to that which is weak, cowardly, or supine. [Century Dictionary, 1895]