equal: the same as something else in measure, in worth, or in standing
This is the ordinary Greek word for equal, and it behaves much like the English one. It holds two things side by side and says they come out the same. What they are the same in depends on what is being compared: the length, width, and height of a city, the amount of a loan paid back, the gift God pours out on one group and then on another, or the place a person holds.
It is a stronger claim than simply saying two things are alike. The nearby word ὅμοιος says one thing resembles another and leaves the closeness open, while this word says the two match. That is why a single use of it can carry an enormous weight. In John 5:18 the charge against Jesus is that he was "making himself equal with God," and the argument of the whole scene turns on that one word.
One use can catch an English reader off guard. At the trial in Mark, the witnesses contradict each other, and the Greek says their testimonies "were not equal." English Bibles rightly say the testimony did not agree, so the word itself disappears from view. The picture behind it is the same measuring idea, two accounts held up beside each other and failing to match, carried out of the marketplace and into the courtroom.
Philippians 2:6 uses an unusual form of the word in the phrase commonly rendered "equality with God," and much of the long argument over that verse runs through it. The word by itself only says equal. Whether the phrase names a standing that Christ already held and refused to exploit, or the way in which he existed, is settled by the sentence around it and not by this adjective. Greek also has a noun built on this word, ἰσότης, for equality or fair dealing considered on its own.
Nuances
How the phrase τὸ εἶναι ἴσα θεῷ in Philippians 2:6 should be construed: as naming equality with God as a status Christ possessed, or adverbially, as describing the manner of his existence.
- majorityThe phrase names equality with God itself, a standing Christ possessed and did not treat as something to be exploited; the neuter plural functions as a normal predicate equivalent to the singular.; BDAG, s.v. ἴσος; P. T. O'Brien, The Epistle to the Philippians, NIGTC (Eerdmans, 1991)
- minorityThe neuter plural is adverbial, describing the mode in which Christ existed, being on a par with God, rather than a status held apart from his self-giving.; C. F. D. Moule, "Further Reflexions on Philippians 2:5-11," in Apostolic History and the Gospel (Paternoster, 1970)