What speakers mean by it now
In present-day English, woman is the ordinary word for an adult female human. It also names women as a class, and it is the second half of many role and nationality compounds, from Englishwoman to sportswoman. Older uses survive at the edges: a female attendant, and, in some dialects, especially in American English, a wife. None of those senses is a late invention. They sit on a native compound assembled before the Norman Conquest and later reshaped until woman / women looked aligned with man / men.
The origin of the word woman is easy to misread from the modern pieces. Seeing wife and man inside it, a later speaker may assume the first meaning was a married woman defined by a husband. That is not how the compound was built. Both halves have narrowed since Old English. The history is those narrowings, plus a vowel that the plural never gave up.
A home-grown compound
Woman was not borrowed from French or Latin. The Oxford English Dictionary treats it as a formation inside English: Old English wīf plus Old English mann. The early written form is wīfmann or wīfman, with wīfmon beside them. Merriam-Webster dates the noun before the twelfth century. Other etymological surveys put related forms in the eighth. Either way, the word belongs to the Old English period, not to Middle English fashion.
Late Old English already shows shortened spellings, wimman and wiman, once the f began to disappear before m. That cluster change is the same kind of smoothing that later turned leofman into lemman. Middle English still offers a swarm of descendants: womman, wimman, wumman, wifman, and regional variants. By about 1400, woman and women had become the regular spellings. The language did not import a new noun. It kept filing down one it already had.
Older general words for a female person did not vanish overnight. Wīf remained available, and quean (from Old English cwene) could still mean a woman before that word darkened. Woman gradually took the central ground those terms had held.
Female person, not wife plus husband
The first element is the ancestor of modern wife. In Old English, wīf was a standard word for a woman or a female person. A marital sense already existed, but it had not yet crowded out the broader one. Religious prose could address a woman as wīf without the modern implication of spouse. That general sense later receded, wife settled on a married woman, and woman became the unmarked adult-female noun.
The second element is mann. Its oldest central meaning was a human being, a person, not an adult male by default. Old English had other words for a male adult, among them wer, which survives mainly as the first half of werewolf. It also had a matching compound wǣpnedmann, a weaponed person, used as the male counterpart to wīfmann. The pair is the clearest evidence of the original design: both were person-words with a sex-marking first element. English kept the female compound and lost the male one. Meanwhile mann drifted toward the adult male while keeping a generic human use. That overlap feeds later arguments about generic man; it is not the sense that went into wīfmann.
Grammatically the compound followed mann. Old English treated wīfmann as a masculine noun even though it named a female person, with the same case pattern as mann, including an i-mutated plural wīfmenn. Feminine agreement is attested now and then, but it is the exception. Later commentators noticed the oddity of joining a neuter noun for a female to a masculine noun for a person in order to name a female exclusively. That is a fair after-the-fact remark. It is not a licence to gloss the compound as wife of a man.
Two older roots
The wīf side goes back to Proto-Germanic wībą, a word for woman or wife. Cognates are still easy to recognize once English specialization is set aside: German Weib, Dutch wijf, and Old Norse víf. In some of those languages the descendant later picked up a blunt or dated tone. The deeper Indo-European source of wībą is uncertain. Proposals have linked it to words for the pudenda, to wrapping or veiling, or to restless movement. None of those accounts is agreed, and a tidy Proto-Indo-European story would be a guess.
The mann side is Proto-Germanic mann-, likewise a person-word, with relatives such as German Mann and Dutch man. A close parallel to the English compound appears in Dutch vrouwmens, literally woman-person and used for a wife. Historical dictionaries note that this formation is characteristic of English and Dutch rather than a pan-Germanic inheritance. Icelandic has a comparable pair in kvenmaður and karlmaður, female person and male person. Germanic speech often marked sex on a person-word instead of inventing an unrelated root.
How the form drifted
Sound, not sense, did most of the visible work after Old English. The rounding influence of w pulled the vowel of the singular. The same rounding is familiar from wood, from Old English wudu, earlier widu. The shift from wi- to wu- is clear around 1200, especially in western texts. Scribes wrote wo- by the late thirteenth century, a common substitution of o for u.
What became standard is a split. The plural women keeps an older i-vowel. The singular settled on the rounded vowel that the w had encouraged. From the fifteenth century the spellings woman and women look like a tidy pair with man and men. In speech they are not a simple copy of that pair. The mismatch is a live remnant of the older wimman / wimmen stage, probably reinforced by other i-mutated plurals already in the language.
Sense history is quieter. Old English already used the compound for a female servant; later English keeps attendant uses. A sense wife is recorded from the mid-fifteenth century and is now largely dialectal. Compounds that mirror those of man stayed productive. Later political uses are new jobs for an old noun, not a new etymology.
The vowel the plural refused to drop
The useful takeaway is not that woman hides man. It is that the hidden first half once meant woman in general, and the second half once meant person. English then specialized both pieces, discarded the male counterpart wǣpnedmann, and froze an older vowel in the plural. Anyone who says women with a short i is still, in that one syllable, closer to late Old English wimmen than the modern spelling of the singular would suggest.