Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!

Gnomish

gad(a)

noun. joint, link; small lane, track; isthmus

A noun appearing as gad or gada in the Gnomish Lexicon of the 1910s based the early root ᴱ√yat- [ẎATA], having several meanings: “joint, link; small lane, track; isthmus” (GL/36).

gada-

verb. to join, connect, unite

A verb appearing as gada- “join, connect, unite” in the Gnomish Lexicon of the 1910s based the early root ᴱ√yat- [ẎATA] (GL/36), with the Gnomish sound change of initial y becoming g.

Neo-Sindarin: The later form of this root is ᴹ√YAT or √YAN, so I would update this verb to ᴺS. ianna- “to join, connect” for purposes of Neo-Sindarin, inspired by the neologism ᴺS. goianna- “join with, add to”. For “unite” I would instead use S. ertha-.

arthaid-

verb. to join

A verb for “to join” in the Gnomish Lexicon of the 1910s formed with the prefixal form of G. artha- “approach” (GL/20). Its second element might be G. gada- “join, connect, unite” (GL/36).