trebly

From treble +‎ -ly.

trebly (comparative treblier or more trebly, superlative trebliest or most trebly)

1. Having treble, or high-pitched, qualities.

trebly (not comparable)

1. (archaic) Three times, thrice
2. To three times the extent or degree; triply.
   • 1883, Robert Louis Stevenson, Treasure Island, Cignet Classic, published 1998, page 13:

     For my part, I must do my best to save this fellow's trebly worthless life; Jim, you get me a basin.

• (three times): thricely, threefold; see also Thesaurus:thrice