A native kinship term
In present-day English, mother names a female parent. The same word also covers people who raise a child without giving birth, and, more loosely, a source, a native language, or anyone who nurtures. That spread of senses is old, but the headword itself is older still. English did not borrow it from French after the Conquest and did not import it from Latin schoolbooks. It was already in the language when English was still Old English.
The origin of the word mother is therefore a story of inheritance, not of fashion. What changed on the surface was spelling and a handful of extra meanings. The kinship sense stayed put.
Old English form and Germanic kin
Old English wrote the noun as mōdor, with variant spellings mōdur, mōder, and mōddor. Middle English normally has moder. Standard dictionaries place the parental sense in English before the twelfth century, which is another way of saying the word is already in the Old English record rather than a later medieval arrival.
Close relatives make the Germanic pedigree obvious: Old Saxon modar, Old Frisian moder, Old Norse móðir, Dutch moeder, Old High German muoter, and modern German Mutter. Those forms reconstruct to Proto-Germanic *mōdēr and, in the west, Proto-West Germanic *mōder. Scots and northern English still keep mither as a regional variant of the same inheritance.
The middle consonant is the part that most needs explaining. The Indo-European kinship word had a *t. Grimm’s Law would ordinarily have turned that stop into a voiceless fricative, the path taken by brother. In the words for mother and father, some inflected forms carried the accent on the suffix, so Verner’s Law voiced the consonant instead. Proto-Germanic therefore had *d, and Old English still spelled a d. In Middle English a group of words shifted spoken -der toward -ther. Spellings with th are already attested in the late fifteenth century; by the early sixteenth they had become the usual written form, catching up with a pronunciation that was probably already current. The same shuffle appears in father, weather, and gather.
German Mutter kept a stop. English wrote a fricative. Both are the same Germanic noun heard through different later sound changes.
The deeper root, and what is still uncertain
Behind the Germanic forms lies Proto-Indo-European *méh₂tēr, the reconstruction that older handbooks often print as *mātēr or *mater-. Cognates are widespread: Latin māter, Greek mētēr, Sanskrit mātṛ, Old Irish máthir, Lithuanian motė, Old Church Slavonic mati. English later borrowed from the Latin branch as well, which is why maternal, maternity, matrix, and matter sit in the same distant family without descending from Old English mōdor.
The suffix is the kinship ending *-ter-, shared with the inherited words for father, brother, and daughter. The first syllable is harder. A long-standing analysis treats it as infant speech of the mā type attached to that suffix. The resemblance to mama-words in many languages makes the idea attractive, and it is still the account most general dictionaries repeat.
Specialists are less unanimous. Balto-Slavic accent points to a laryngeal in the root, not a simple baby-talk long vowel, and some reconstructions prefer a real verbal stem with a sense along the lines of nursing or mothering. If the word is a nursery formation after all, at least one careful reconstruction would rather start from *mah₂tēr than from a tidy *mā- plus suffix. The kinship ending is not in doubt. The exact history of the first syllable is.
Albanian shows how even a stable inheritance can drift: motër, from the same root, means sister rather than mother.
Meanings that grew around the parent
The parental sense never dropped out. Around it, English built a set of figures that treat origin as birth. Late Old English already used the noun for whatever had given rise to something. By about 1200 it could address an older woman, often as a familiar or class-marked form of speech. Mother tongue, for a native language, is recorded from the late fourteenth century. Mother-wit, native common sense rather than book learning, appears in the mid-fifteenth. Personifications such as Mother Nature, from the 1550s, and mother earth, from the 1580s, push the same metaphor outward, as does mother country in the same decade, for a land in relation to its colonies.
The verb follows the noun. An intransitive use, to be a mother, is found in the early fifteenth century; a transitive use, to be the mother of, in the mid-sixteenth; to care for someone as a mother would is later still, from the nineteenth century.
One side sense remains genuinely unsettled. Mother can also name the stringy film that forms in fermenting wine or cider and turns alcohol into vinegar. One standard etymological dictionary derives that sense from Middle Dutch modder, a word for filth or dregs, related to mud. Other references note that Dutch, German, French, Italian, and Spanish all use their ordinary mother-words for the same vinegar culture, which would make the English sense a natural extension of the kinship noun rather than a borrowing. Both accounts cannot be simply true at once. The vinegar use is real; its source is not settled.
A consonant that still carries the date
The most concrete leftover of this history is the th in the modern spelling. It is not an original Indo-European fricative. It is a Middle English way of writing a voiced sound that began as Proto-Germanic *d, itself a Verner outcome of an older *t. Look at German Mutter beside English mother and the kinship is still audible, once that one sound law is allowed for.