Second person singular present tense of 'care' in archaic or poetic English; you care (as in 'thou carest').
From Old English 'carian', related to Old Norse 'kǫrr' (care, sorrow). The '-est' ending is the archaic second person singular form used with 'thou' in Early Modern English.
Shakespeare and the King James Bible used 'thou carest' constantly, but this form disappeared after about 1700 when 'thou' itself became archaic—yet you can still spot it in prayers and period fantasy novels to create an 'old' feeling.
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