In the book 'The Lombard Laws' (Fischer Drew; 1973), footnote 43, on page 245; it states regarding the "thinx":
"The thinx was, properly speaking, the public assembly, ding, of the Lombards. After the settlement in Italy, however, the wide scattering of the Lombard people would have made such a general assembly impossible.
Hence the witnessing of contracts--an important function of the assembly--was transferred to a smaller group of witnesses. "The gairethinx ("spear assembly") name remained, however, and from this word the shorter form thinx was often used to refer to the formal contractual procedure of gairethinx, or even to the gift, the object of the transfer, itself."
Gairethinx (from Wikipedia):
The gairethinx was a Lombard ceremony in which edicts and laws were affirmed by the army. It may have involved the entire army banging their spears on their shields. It may have been a much quieter event.
It is etymologically related to the Thing of the Vikings and Anglo-Saxons and the Althing of Iceland.