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Webster 1828 Edition

adv.

Not seasonably; not in due time, or not in the usual time; not in the time best adapted to success.

unseasonably ‎(not comparable)

Not in accordance with the season.
- 1960, Alfred Stefferud, Yearbook of Agriculture (page 188)
  Long periods of unseasonably humid weather may make it difficult to complete drying quickly enough. Many farmers are using supplemental heating equipment to avoid this possibility.