Now faith is the assurance of things hoped for, the conviction of things not seen

Substance: hypostasis
1) a setting or placing under
a) thing put under, substructure, foundation
2) that which has foundation, is firm
a) that which has actual existence
1) a substance, real being
b) the substantial quality, nature, of a person or thing
c) the steadfastness of mind, firmness, courage, resolution
1) confidence, firm trust, assurance

Hebrews 11:1 ESV