Meaning of -EST in English

-EST

[-est] adj suffix or adv suffix [ME, fr. OE -st, -est, -ost; akin to OHG -isto (adj. superl. suffix), Gk -istos]--used to form the superlative degree of adjectives and adverbs of one syllable "fattest" "latest", of some adjectives and adverbs of two syllables "luckiest" "oftenest", and less often of longer ones "beggarliest"

[2]-est or -st vb suffix [ME, fr. OE -est, -ast, -st; akin to OHG -ist, -ost, -est, 2d sing. ending]--used to form the archaic 2d person singular of English verbs (with thou) "didst"

Merriam-Webster English vocab.      Английский словарь Merriam Webster.