A word for “fruit drink, cider” in a rough notes from 1940, whose primitive form was {ᴹ✶yābā-sāb >>} ᴹ✶yābā-sūka and whose Old Noldorin form was ON. {yōbasoka >>} yōbasūka > iovhug > iofog (TMME/53). It was thus a combination of the ancient roots ᴹ√YAB “fruit” and ᴹ√SUK “drink”, though the deleted primitive form indicates Tolkien first considered ᴹ√SAB “juice” as the basis for the second element.
The change of o to ū in the Old Noldorin form could represent vacillation between ᴹ√SOK and ᴹ√SUK as the root for “drink”. However, since primitive long ō became ū in Old Noldorin, it is hard to say what the exact vowel in the root was. In the initial syllable ᴹ✶yābā, ancient long ā became ǭ and then au, but then the au became o as usual in polysyllables to produce iov-. This reduction of au to o also allowed the v from b to survive. Compare this to monosyllabic N. iau < ✱yābē where the v was lost after au (Ety/YAB).
Note that the change of u to o in the final syllable of this word is unusual. In Noldorin (and Sindarin), the change of short ŭ to o was normal, but an ancient long ū usually meant the u survived. For example, compare this to N. gwanur < ON. wanūro from The Etymologies (Ety/TOR). The survival of h in iofhug is also unusual, since generally the loss of h between vowels occurred before short vowels vanished before morpheme boundaries, as with the development of the name N. Tinúviel. Thus we would expect iauvahūg to become (perhaps) iovaug, not iovhug. However, perhaps the h in iofhug was restored by analogy with the mutated forms of independent words like N. sog- “drink”.
Neo-Sindarin: For purposes of Neo-Sindarin, I would retain this word as iofog, but would assume the primitive form was ✱yāba-sŭka or ✱yāba-sŏka to avoid the question of the abnormal development of ū > o. I think both [yofog] and [yovog] are acceptable pronunciations.
For the second meaning, cf. Hadorion, a Húrin's epithet in WJ/294, Hurinionath referring to the house of Húrin the Steward in PM/202-3,218, and Gil-Galad's epithet Ereinion, cf. also the gloss of the old Qenya cognate yondo "descendant of" in PE/12:106, or the use of the same suffix in later Quenya names such as Isildurioni and Anárioni "Heirs of Isildur (resp. Anárion)" in PM/192,196