The Proto-Indo-European word *ténus
Word *ténus
Meaning long, thin
See also Homeric Greek: τανύω ‘stretch, strain’
Synonyms *dluh₂gʰó-, *dl̥h₁ghós, *dlonghos, *kr̥k̂ós, *mak-, *skidrós, *makrós, *seh₁ros

Comments
Lat. tenuis, Ir. tanae/tana, OCS tĭnŭkŭ, Russ. tonkij, Skr. tanu, Gk. tanus, Eng. þynne/thin, Gm. thunni/dünn, Polish cienki, ON þunnr, Av. tanū, Pers. /tan, Lith. teva, Ltv. tievs

Other words that might be of interest
*mel- ‘strong, big’, *pau- ‘small’, *mei- ‘small’, *meĝ- ‘great’, *mreĝʰú- ‘short’, *were- ‘wide, broad’, *ānos ‘circle, ring’, *h₃érbʰis ‘circle, orb’, *wérhₓus ‘broad, wide’, *meĝha- ‘large, great’, *mr̥ĝhus ‘short’, *pau- ‘little, few’, *pl̥th₂ú- ‘wide, broad’