Thrice means three times, in old use. Thrice daily, thrice blessed, thrice over.
It is archaic in ordinary English and survives in fixed phrases and deliberate flourish — three times is what people actually say. It belongs with once and twice, which survived while thrice did not, and no English word ever existed for four times. Note that thrice is three plus the old ending -es that also made once and twice.
1adverbthriceThree times, in old use.
“In the old tale, the knight knocked thrice on the castle gate.”
thrice is a count of repetition.
Middle English thries is three plus the adverbial ending -es. Once and twice are formed the same way.
Proto-Indo-European
*tréyes
Old English
þriwa
Middle English
thrice
English, today
thrice
Built from
From Middle English thrice, thries (“three times, thrice; a third time; repeated three times”), from earlier thrī, thrīe (“three times, thrice; a third time”) (from Old English þriwa, þreowa) + -es (from Old English -es). The word is cognate with Old Frisian thria "thrice"; > stq träie (“thrice”), Middle Low German drîes (“thrice”), Middle High German drīes, drīs (“thrice”).
Etymology from Wiktionary, CC BY-SA