"Conociste" is not english. It is the verb "to know" in spanish. Informal second-person singular (tú) preterite indicative form conocer ( to know, in english). http://en.wiktionary.org/wiki/conociste

Tú conociste = Thou knewest (Past form, Old English) We do not use this old form for thou in Modern English. We use "you" instead of "thou" all time at present.

You will not find this word in a dictionary because it is the verb know, which is conjugated in the past tense or past asi: - yo conocí - tú conociste - el/ella conoció - nosotros conocimos - vosotros conocisteis - ellos/ellas conocieron

another good online dictionary where you can find all differents spanish conjugation forms directly translated to english is www.wordreference.com