If Terhenetär comes from terho (acorn), it means a lady/woman of acorn (-tär is a feminine ending like -ess in actress). But it's more possible that it comes from terhen whitch means mist, and as you add -tär in the end, it means a lady/woman of mist. [noted -ed]
-- Anonymous User 2/13/2007
In the Finnish language "terhen" means a light mist, and Terhi most probably derives from this and has nothing at all to do with acorns. [noted -ed]