The Oxford Names Companion, OUP "Scottish Forenames" - Donald Whyte, FGH, FSG Personal correspondence [VC]
Notes:
English, Italian and and Spanish from Latin "of the wood". This is the same meaning of the male name Silvester but the names are not associated in the sources.
Silvia was the original English spelling but Sylvia is now preferred.
Thanks to Donald Whyte who provided much of the initial information for this site.