third: the one that comes third in a counted order
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This is the ordinary ordinal number "third," the counting word that marks where something falls in a sequence. It is built from the same root as the cardinal "three," but where "three" answers how many, "third" answers which one in order.
Its most common job is dating: the third day, the third month, the third year, the third generation. Genesis opens its account of creation with "the third day," and the calendar laws repeatedly fix festivals and offerings to a third day or third year. It also ranks people and things in a line: the third son, the third captain, the third division of an army, the third tier of a building. In every case the word simply says "number three in this series," and a reader loses almost nothing by rendering it "third."
a third part: one of three equal shares; one-third
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The same word, in its feminine form, can name a fraction rather than a position: a third part, one of three equal pieces. Hebrew often turns an ordinal into the matching fraction this way, so the form that means "third" also serves for "a third."
The priestly laws use it for measured amounts, such as a third of a hin of wine or oil poured out with an offering, or a third of a shekel given each year for temple upkeep. The prophets use it for groups of people or things split three ways: Ezekiel divides the city's people into thirds for the sword, famine, and scattering, and Zechariah speaks of a remnant third refined like silver in the fire. The line between this fraction and the plain ordinal is real but thin, since both grow from the idea of three; the reader is helped by noticing whether the text counts a position (the third day) or measures a share (a third of the people).
Marks the measured third part of priestly offerings, the fixed cultic ration of flour, oil, or wine that the law prescribes for sacrifices.Num 15:6Num 28:14Ezk 46:14
Divides an army or a body of people into thirds for battle and organization, a tactical sense rooted in Israel's military and administrative life.2Sa 18:22Ki 11:5
Labels a structural level of a building, the third story, as in the decks of the ark and the side chambers of Solomon's temple.Gen 6:161Ki 6:61Ki 6:8
Both
Both are the plain ordinal that orders a sequence of days, the next step after the first and the second.Gen 22:4Luk 13:32
Both name a deliverance or turning point set for the third day, when something decisive happens after two days of waiting.Hos 6:2Luk 24:46
Both can mean a third part, a fraction of a whole, whether measured out for worship or struck in judgment.Num 28:14Rev 8:7
Carries a fixed theological weight in the phrase "the third day," the set time the New Testament announces for the resurrection: Jesus foretells being raised on the third day, and the early preaching repeats it as a settled fact.Mat 16:21Luk 24:71Co 15:4
Becomes a recurring unit of doom in Revelation's trumpet visions, where a third of the earth, sea, rivers, sun, and even the stars is struck, a measured but devastating fraction of judgment.Rev 8:7Rev 8:9Rev 9:18Rev 12:4
Names a place rather than a count in the phrase "the third heaven," Paul's term for the highest realm to which he was caught up.2Co 12:2
What scholars say about shelishi
Standard lexica (BDB, HALOT, DCH) treat שְׁלִישִׁי as the ordinal of the cardinal שָׁלוֹשׁ "three," used adjectivally for the third in a series and substantivally for dates and ranks. They also recognize the feminine שְׁלִישִׁית as a fraction, "third part," in cultic measures (a third of a hin, a third of a shekel) and in prophetic divisions of people into thirds (Ezekiel 5; Zechariah 13). A handful of forms tagged here are textually or lexically separate: the form שְׁלִשִׁיָּה in Isaiah 15:5 and Jeremiah 48:34 belongs to the place name Eglath-shelishiyah (or is read as a heifer of three years), and the difficult שְׁלִשִׁתָה in Ezekiel 21:14 is variously analyzed; these are left unclassified rather than forced into a sense.