Hi Patrick,

I think that siddha and jīvanmukta are certainly not synonyms. Siddha may refer to a class of semi-divine
beings, as well as to adepts who have obtained mundane siddhi but who are by no means "liberated."
In Buddhist usage mahAsiddha refers to one who has obtained the "supreme siddhi" - enlightenment -
and so this may be synonymous with jīvanmukta.

Some of the works of David White (esp. The Alchemical Body), may also be helpful here. Ronald Davidson's
Esoteric Buddhism in India and Christian Wedemeyer's recent Making Sense of Tantra may be useful on
the Buddhist side. There's certainly much more, particularly in the literature on Kashmir Saivism,
but this is at least a start.

Matthew