predominantly

predominant +‎ -ly

predominantly (comparative more predominantly, superlative most predominantly)

1. In a predominant manner. Most commonly or frequently by a large margin.

   The membership is predominantly elderly, 90% are over age 60.

   • 1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, New York, N.Y.: Columbia University Press, →ISBN, page 3:

     Both groups are predominantly confined to areas with warm to tropical climates […]

This adverb form of the adjective predominant is preferred over predominately (the adverb form of the adjective predominate), which is considered dated or non-standard.

• primarily, principally; see also Thesaurus:mostly or Thesaurus:usually