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Webster 1828 Edition

Noun.

Thinness; smallness of diameter in proportion to the length; as the slenderness of a hair.

Want of bulk or strength; as the slenderness of a cord or chain.

Weakness; slightness; as the slenderness of a reason.

Weakness; feebleness; as the slenderness of a constitution.

Want of plenty; as the slenderness of supply.

Spareness; as slenderness of diet.

slenderness ‎(usually uncountable, plural slendernesses)

The property of being slender.
- 2015 June 9, “Women’s World Cup 2015: England beaten by France in Group F opener”, in The Guardian (London):
  England have not beaten their neighbours from across the Channel since 1974 and the slenderness of the scoreline, with the two side’s separated only by Eugénie Le Sommer’s first-half strike, disguises the superiority of a French side now clear favourites to top Group F

property of being slender