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Webster 1913 Edition

Noun.

Want of thrift; unthriftiness; prodigality.

An unthrifty person.

[Obs.]

Dryden.

Adj.

Unthrifty.

[Obs.]

Noun.

A prodigal; one who wastes his estate by extravagance.

unthrift ‎(plural unthrifts)

A lack of thriftiness; prodigality.
(now rare) Someone who is not thrifty; a spendthrift, someone who is not careful with their money.
- 1633, John Donne, "The Autumnall":
  But name not Winter-faces, whose skin's slacke; / Lanke, as an unthrifts purse [...].

unthrift ‎(comparative more unthrift, superlative most unthrift)