Could Proto-Germanic *tīhaną be an ē-grade of *tungǭ zero-grade?
Gothic has -h- / -ng-:
- huhrus – huggrjan
- juhiza – juggs
- ga-teihan – tuggo ?
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Sign up to join this communityIt is of course right that Gothic has Verner's Law variants -χ- / -ng- (spelled <h> /<gg>, respectively), as seen in your first two examples.
It is also right that tuggo has a zero grade root. However, gateihan cannot be an ē-grade, as PIE *-ē- will develop to PGmc. *-ē₁-, which will result in Gothic -ē- as in Gothic nemun '(they) took' (from niman 'to take). The verb gateihan rather has the regular e-grade root (full grade), which in the present/infinitive of a strong verb of class I is regularly represented by -ī- (spelled <ei>), < PGmc. *-ī- < *-ei-.
So I guess that your real question is whether PGmc. *tīχan- 'to announce' could be the e-grade and PGmc. *tungō- 'tongue' the zero grade of one and the same root. The answer to this is no, at least according to standard textbook knowledge. The 'tongue' word is a cognate of Latin lingua < Old Latin dingua < PIE *dn̥ǵʰweh₂- (Casaretto 2004: 230). This is considered to be a pure nominal stem, without a verbal root. PGmc. *tīχan- is derived from the verbal root PIE *deyḱ- 'to show' (Lehmann 1986: 150) and compared to Latin dīcō 'I speak' etc. These two reconstructions are not reconcilable.
References
Casaretto, Antje (2004). Nominale Wortbildung der gotischen Sprache. Die Derivation der Substantive. Heidelberg: Winter.
Lehmann, Winfred P. (1986). A Gothic Etymological Dictionary. Leiden: Brill.