The NeoQuenya and NeoSindarin Wiktionary
tercara (tercare)
Prep ter(e)- 'through' (Etym) + cara 'doing'
Cf. ilúcara 'omnificent' (VT39); tercen 'insight, through-sight'
*tercarya cf. saucarya 'evil-doing' (PE17)
Tamas Ferencz, Alexander Zapragajev