regnant

1. Reigning; ruling: a queen regnant.
2. Predominant.
3. Widespread; prevalent.

[Probably from Middle English, a sovereign, from Old French, from Latin rēgnāns, rēgnant-, present participle of rēgnāre, to reign, from rēgnum, reign. See reign.]

adjective

1. Exercising controlling power or influence: commanding, controlling, dominant, dominating, dominative, governing, paramount, preponderant, reigning, ruling. See over/under.
2. Having preeminent significance: ascendant, dominant, predominant, prepotent, prevailing, ruling, supreme. See important/unimportant.
3. Most generally existing or encountered at a given time: current, predominant, prevailing, prevalent, rife, widespread. See specific/general.

The adjective has one meaning:

Meaning #1: exercising power or authority
  Synonyms: reigning, ruling