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Webster 1913 Edition

Adj.

(Math.)

Indicating one part of two; in the ratio of one to two.

Subduple ratio

the ratio of 1 to 2: thus, 3:6 is a subduple ratio, as 6:3 is a duple ratio.

Adj.

[L., double.] Containing one part of two.

subduple ‎(not comparable)

(mathematics) Indicating one part of two; in the ratio of one to two.
3:6 is a subduple ratio, while 6:3 is a duple ratio.
- Bishop Wilkins
  As one of these under pulleys abates half of that heaviness of the weight, and causes the power to be in a subduple proportion; so two of them abate half of that which remains, and cause a subquadruple proportion, three a sextuple, four a suboctuple.