Once
'echad (ekh-awd')
united, i.e. one; or (as an ordinal) first
have I sworn
shaba` (shaw-bah')
propr. to be complete; to seven oneself, i.e. swear (as if by repeating a declaration seven times)
by my holiness
qodesh (ko'-desh)
a sacred place or thing; rarely abstract, sanctity -- consecrated (thing), dedicated (thing), hallowed (thing), holiness, (most) holy (day, portion, thing), saint, sanctuary.
that I will not lie
kazab (kaw-zab')
to lie (i.e. deceive), literally or figuratively -- fail, (be found a, make a) liar, lie, lying, be in vain.
unto David
David (daw-veed')
loving; David, the youngest son of Jesse -- David.