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Webster 1913 Edition

adv.

Not thriftily.

Improperly; unbecomingly.

[Obs.]

Chaucer.

adv.

Without frugality.

unthriftily ‎(comparative more unthriftily, superlative most unthriftily)

In a way that is not thrifty.
(obsolete) In an improper or unbecoming manner.
(Can we find and add a quotation of Chaucer to this entry?)