Note: the obsolete adjective definition is a general sense.
In mathematics, it is applied to the proportion of two quantities one of which is double of the other;
in music, it is applied to ‘time’ or rhythm having two beats in the bar.
ETYMOLOGY
Adj. and n.: from Latin duplus (double), from duo (two) + -plus, from root ple- (to fill);
Vb.: from Latin duplare (to double), from dupl-us (duple)
EXAMPLE (for vb.)
“… She mixd of Quick-silver a deadly weight,
That dupled force his murder hasten might.
Then while those baneful pots betwixt them strov,
The helpful swaying the hurtfuls bane out drov. …”
From: Enchiridium epigrammatum Latino-Anglicum:
An epitome of essais,
Englished out of Latin by Robert Vilvain, 1654
Lexicophilia 