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Webster 1913 Edition

(-fụl-ly̆)

adv.

Peevishly; vexatiously; detestably.

[Obs.]

“Curstfully mad.”

Marston.

curstfully ‎(comparative more curstfully, superlative most curstfully)

(obsolete, nonce word) peevishly; vexatiously; detestably
- Marston
  curstfully mad