In proper sequence or arrangement, as in The children lined up in order of size, or Are the letters all in order? [c. 1400]
Suitable, correct, appropriate, as in A few words on this subject are in order now. [Mid-1800s]
See in short order.
in order that. So that, to the end or purpose that, as in In order that Bob can meet my husband, we've come early. [Early 1700s]
in order to. For the purpose of, as a means to, as in We'll have to hire more help in order to finish on time. This usage always precedes a verb, such as finish in the example. [c. 1700]