A verb in The Etymologies of the 1930s glossed “bind” appearing in its (Noldorin) infinitive form gwedi, with an archaic past form gwend/gwenn and a later past gweðant, all under the root ᴹ√WED “bind” (Ety/WED). Given its root, the expected stem form would be *gwedh-, so the form gwedi is probably either archaic or malformed.

Neo-Sindarin: For purposes of Neo-Sindarin, I would assume its stem form was gwedh-, and I would modernize its past forms as described in the entry on the Sindarin past tense.