adverb
easily; comfortably; well over
Used with quantities to indicate that a number or amount is reached or exceeded with room to spare. Often translates as 'a good ...', 'no less than ...', or 'easily ...'.
その荷物は優に20キロはある。
That luggage easily weighs 20 kilograms.
会場には優に1000人以上の人が集まった。
Well over 1,000 people gathered at the venue.
彼の年収は優に1000万円を超える。
His annual income comfortably exceeds 10 million yen.
Means 'at least' and sets a minimum, while 優に implies the amount is reached with ease and often suggests a generous margin.
Derived from the kanji 優 (yū, 'superior, gentle') used adverbially. The exact historical derivation is uncertain, but it has been used since at least the Edo period to express abundance or ease in reaching a quantity.