noun
usual; stereotyped; predictable
Often used with a slightly negative nuance to describe something that is trite, clichéd, or predictably routine. Common in phrases like お定まりのパターン (the usual pattern) or お定まりの文句 (the same old line).
彼のスピーチはお定まりの内容だった。
His speech was the usual predictable content.
またお定まりの言い訳か。
The same old excuse again, huh?
いつも通り is a neutral expression meaning 'as usual' without the negative or stereotyped nuance of お定まり.
定番 refers to a standard or classic item, often with a positive connotation of reliability, unlike the often negative お定まり.
From the honorific prefix お (o-) attached to the noun 定まり (sadamari, 'fixed thing, rule'), the nominalized form of the verb 定まる (sadamaru, 'to be decided, to be fixed').