-est1

1.
a suffix forming the superlative degree of adjectives and adverbs:
warmest; fastest; soonest.
Origin
Middle English; Old English -est, -ost. Compare Greek -isto-

-est2

1.
a native English suffix formerly used to form the second person singular indicative of verbs:
knowest; sayest; goest.
Also, -st.
Origin
Middle English; Old English -est, -ast, -st, 2nd person singular present indicative endings of some verbs (-s earlier verbal ending + -t, by assimilation from thū thou1) and 2nd person singular past endings of weak verbs (earlier -es + -t)
British Dictionary definitions for -est

-est1

suffix
1.
forming the superlative degree of adjectives and adverbs: shortest, fastest
Word Origin
Old English -est, -ost

-est2

suffix
1.
forming the archaic second person singular present and past indicative tense of verbs: thou goest, thou hadst
Word Origin
Old English -est, -ast