springhead
ur-source
mother
straight from the horse's mouth
emanate
root
from good hands
firsthand
at first hand
last word
reference
trufax
authorship
title
give birth
magisterium
underpinning
have something on good authority
founded
scripture
oroclinal
wartweed
factualist
fons et origo
factically
factually
outpart
matter of fact
thus
assertedly
font
relevantly
uredosporous
dead-on
by
uredosporic
⠁⠉
uredinous
uredineous
intersource
afore-explained
foundation stone
forenote
strike
grass roots
clue
materially
bairn's part
basics
rudiments