bigtime

/B IH1 G T AY0 M/
noun
  1. 1

    The highest, or most prestigious level in any field, especially in entertainment.

adjective
  1. 1

    Of major significance or importance.

Antonyms

adverb
  1. 1

    To a significant degree.

Source: https://en.wiktionary.org/wiki/big%20time, https://en.wiktionary.org/wiki/bigtime