plural of double factorial

(mathematics, combinatorics) For an odd integer, the result of multiplying all the odd integers from 1 to the given number; or for an even integer, the result of multiplying all the even integers from 2 to the given number; symbolised by a double exclamation mark (!!). For example, 9!! = 1 × 3 × 5 × 7 × 9 = 945.

Involving both hands. / Designed to be used with two hands. / Involving two people. / Serving two purposes or involving two approaches. / deceitful; deceptive

With two hands.

simple past tense and past participle of double-hand

(music) Of a note, having a duration of 1¾ times its basic note value. / (linguistics) Of a character, having a diaeresis/umlaut/rock dots

(darts) Double twenty (on a dartboard).

A number composed of two digits, i.e. between 10 and 99.

plural of double door: Multiple sets of paired doors.

Synonym of double door: A set of two adjoining doors that can be opened independently.