sunkus (“heavy, difficult”) + -ai <span class="searchmatch">suñkiai</span> (comparative sunkiaũ, superlative sunkiáusiai) heavily with difficulty “<span class="searchmatch">sunkiai</span>”, in Lietuvių kalbos žodynas [Dictionary...
to breathe lengvas (Nouns) sunkýbė f sunkumas m sunkvežimis m (Adverbs) <span class="searchmatch">suñkiai</span> sunkỹn keblus ^ Wojciech Smoczyński (2018) “sunkus”, in Lithuanian Etymological...