From WordNet (r) 2.0 (August 2003) [wn]:
headspring
n : the source of water from which a stream arises; "they
tracked him back toward the head of the stream" [syn:
fountainhead, head]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Headspring \Head"spring`\ (h[e^]d"spr[i^]ng`), n.
Fountain; source.
[1913 Webster]
The headspring of our belief. --Stapleton.
[1913 Webster]