What it counts today
Seven is the English name for the integer after six. Speakers also use it for the written digit, for a card with seven pips, and, in everyday time-telling, for seven o'clock. Those extra jobs are thin extensions of one stable sense. Unlike many common English words, this one did not wander far from its original meaning. It has named the same number for as long as English has been written.
Inherited from Old English
The origin of the word seven is native Germanic inheritance, not a borrowing from French or Latin. Old English wrote seofon, with regional variants such as seofun and syfon in Late West Saxon, siofun in Mercian, and shorter Northumbrian forms seofo, siofu, and sifu. Middle English spellings cluster around seven, sevene, seoven, and Kentish zeven. Historical dictionaries date the English form before 900 because Old English texts already contain it; the numeral was not coined in Middle English.
From Old English the line runs back through Proto-West Germanic sebun to Proto-Germanic sebun. The same ancestor yields Gothic sibun, Old High German sibun, written by the eighth century, Old Saxon sibun, Middle Dutch seven, Dutch zeven, and German sieben. North Germanic went its own way: Old Norse sjau, Swedish sju, Danish syv, Icelandic sjö. Scholars often treat the Old Norse shape as analogical, pulled toward the neighboring word for eight.
The Indo-European numeral
Beyond Germanic the picture is still one family. Latin septem, Ancient Greek hepta, Sanskrit sapta, Avestan hapta, Hittite shipta, Old Church Slavonic sedmi, Lithuanian septyni, Old Irish secht, Welsh saith, and Russian sem all continue a Proto-Indo-European cardinal reconstructed as septm. English seven is the Germanic child of that root. Learned English words built on the Latin or Greek forms — September, septet, septennial, heptad — arrived later and sit beside the native numeral rather than explaining it.
Germanic is the odd branch in one respect: it lacks the inner dental that Latin and Sanskrit keep. That loss is agreed; the reason is not. One long-standing account is dissimilation. The cardinal was reshaped under pressure from an ordinal that also contained a t, so two dentals in close quarters were reduced. Another reconstruction of Proto-Germanic works from an earlier sebunt, itself from a Pre-Germanic rearrangement of the older form, with the t aligned analogically on nine and ten. A third suggestion traces that extra t to the Indo-European ordinal. None of these stories is a closed case, and it would be dishonest to present one as the only path.
A separate hypothesis, found in comparative handbooks rather than in ordinary English dictionaries, notes that the Indo-European numeral resembles the Proto-Semitic word for seven and may have been a culture word moving around the ancient Near East. That idea, if it is ever proved, would concern the remote prehistory of the Indo-European form. It does not change the English history: seven still comes down through Germanic, not through a later Semitic loan into English.
How the sounds line up
The consonants that English kept are the expected Germanic outcomes. The Indo-European p became f under Grimm's law, then voiced to b under Verner's law in this word because of the accent pattern of the numeral. In English, that b between vowels later became v, which is why seofon is seven while German sieben still shows b. The Old English diphthong eo is a regular breaking of an older front vowel before the following consonant. There is no prefix or suffix hiding in the modern spelling. Seven is a simplex. The ordinal seventh and the compounds seventeen and seventy are built on it in the ordinary Germanic way.
What the meaning did not do
Because the counting sense never cracked, later uses are almost all metonymy. By the late fourteenth century, seven could name a throw at dice. By the early fifteenth it could mean the hour. Older English sometimes used it with days or years as a round figure for a long stretch, not a measured week or year. Fairy-tale seven-league boots treat it as a measure of extraordinary distance. Old English sibunsterri, the seven stars, usually meant the Pleiades; from the fifteenth century the same name was sometimes given to the Plough, which also has seven bright stars, or to the seven planets of classical astronomy.
Lists of sevens — wonders, sleepers, sages, deadly sins — made the number a symbol of completeness in Christian and classical culture. Etymological surveys treat that symbolism as late in Old English, not as the force that created the word. Folk belief later credited healing power to a seventh son. Early modern German could call a difficult woman an evil seven, which is a useful reminder that the numeral was not locked to luck or holiness.
The Latin look-alike
The fact worth keeping is the mismatch with Latin. Septem and seven are the same Indo-European numeral, yet they do not look like twins until the history is unpacked. September on a calendar is a learned borrowing that still carries the Latin t. Seven is the native form that dropped that dental, voiced the stop, and went on counting from six to eight without leaving Germanic.