1) Backbone 2) Core 3) Egohood 4) Essence 5) Essential part 6) Essentialness 7) Gist 8) Heart 9) Important part 10) Inbeing 11) Incarnation 12) Inherence 13) Inhesion 14) Lifeblood 15) Marrow 16) Noumenon 17) Pith 18) Quiddity 19) Quintessence 20) Soul 21) Subjectiveness 
• (n.) The quality of being intrinsic; essentialness; genuineness; reality.
In·trin`si·cal'i·ty noun The quality of being intrinsic; essentialness; genuineness; reality.