the real being or substance of something: what it actually is beneath how it appears
The oldest and most concrete idea behind this word is something that stands underneath. In ordinary Greek it named the sediment that settles at the bottom of a liquid, the foundation under a building, or a garrison holding its ground. From there it grew into a word for what is really there, as opposed to what only seems to be there.
Hebrews 1:3 uses it in exactly that deeper sense. The Son is the exact imprint of God's real being, the stamp that shows what God actually is. Here the word points to God's essential nature, not to a physical substance and not to a "person" in the sense the church later gave that word.
Hebrews 11:1 stretches the same idea to its limit: faith is called the substance of things hoped for, set beside the proof (ἔλεγχος) of things not seen. On the reading most scholars now favor, faith is the reality of what is hoped for, the unseen future made solid and present. Others hear a more personal note of "assurance" in the same word (see the next meaning). It is the single most argued word in the sentence.
Nuances
What faith is said to be, relative to things hoped for, in Hebrews 11:1.
- contestedFaith is the objective reality of what is hoped for, the coming realities made present, parallel to the "real being" of God in Hebrews 1:3.; H. Koester, 'hypostasis', TDNT 8:585-588; L. T. Johnson, Hebrews (NTL, 2006), 277-282
- contestedFaith is the subjective assurance or confidence that grasps what is hoped for.; P. Ellingworth, Hebrews (NIGTC, 1993), 565-566; F. F. Bruce, Hebrews (NICNT, rev. 1990), 277-278
- minorityFaith is the title-deed or guarantee that secures a future possession, a sense drawn from the property documents of the Greek papyri.; J. H. Moulton and G. Milligan, Vocabulary of the Greek Testament, s.v.; BDAG (3rd ed., 2000), s.v.
- minorityThe word works by metonymy, naming both the objective reality and the assurance that reality produces.; H. Attridge, Hebrews (Hermeneia, 1989), 307-310; C. Koester, Hebrews (AYB, 2001), 472