doubly, so as to make sure, so that there be absolutely no doubt / absolutely! with pleasure! yes please!

a set of double doors

(simile) like two peas in a pod; exactly alike

(informal) in no time, in two shakes, in a flash, in a jiffy

(figuratively) to make ends meet

plural of porte à deux battants

(informal) to be all thumbs, to be very clumsy

it's one of those two things; there are two possibilities, there are two possible scenarios; you have two options; you choose(: either ... or)

(informal) not ... at all, not ... in the least

(figuratively) to fall between two stools, to have a foot in both camps, to be piggy in the middle, to be caught in the middle, to be sitting on the fence