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]

early 15c., "dissolved, of loose structure," also "morally lax" (senses all obsolete), from Latin resolutus, past participle of resolvere "untie, unfasten, loose, loosen" (see resolve (v.)).

It emerged c. 1500 in the sense of "determined, decided, absolute, final," especially in the phrase resolute answer, which was "common in 16th c." [OED]. The notion is of "breaking (something) into parts" as the way to arrive at the truth of it and thus make the final determination (compare resolution).

The word has been used from 1530s of persons, "determined in mind, having a fixed resolve." Related: Resolutely; resoluteness. In Middle English a resolutif was a medicine to dissolve and disperse hardened matter (c. 1400).

in prosody, a foot of two syllables, the first short or unaccented, the second long or accented, 1842, from French iambe (16c.) or directly from Latin iambus "an iambic foot; an iambic poem," from Greek iambos "metrical foot of one unaccented followed by one accented syllable" (see iambic). Iambus itself was used in English in this sense from 1580s. In Greek, the measure was said to have been first used by satiric writers.

[The Iambus] is formed constantly by the proper accentuation of familiar, but dignified, conversational language, either in Greek or English : it is the dramatic metre in both, and in English, the Epic also. When the softened or passionate syllables of Italian replace the Latin resoluteness, it enters the measure of Dante, with a peculiar quietness and lightness of accent which distinguish it, there, wholly from the Greek and English Iambus. [Ruskin, "Elements of English Prosody, for use in St. George's Schools," 1880]