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Webster 1913 Edition

Noun.

The quality, condition, or state, of being straight;

as, the

straightness

of a path

Noun.

A variant of

Noun.

The quality or state of being straight; rectitude.

Narrowness; tension; tightness.

straightness ‎(countable and uncountable, plural straightnesses)

(uncountable) The state or quality of being straight (especially in the sense of "heterosexual").
(countable) The result or product of being straight.