The Sindarin word for “father”, derived from the root √AT(AR) (PM/324; VT44/21-22; VT48/19).
Conceptual Development: N. adar “father” also appeared in The Etymologies of the 1930s as a derivative of the root ᴹ√ATA of the same meaning (Ety/ATA). In the Gnomish Lexicon of the 1910s, however, G. †ador “father” was marked as archaic, and it seems {athon >>} G. nathon was the ordinary word for ”father” (GL/17, 59).
A play-name for thumb, as well as an affection word for “father”, in notes Elvish Hands, Fingers and Numerals from the late 1960s (VT48/6). It is a combination of the root √AT with the diminutive suffix -eg. Tolkien considered but rejected several alternate forms including aderig and tadeg (VT48/17 note #13).