In the context of writing and speaking, expand and elaborate (both usually followed by “on”) refer to saying more about an idea, topic, or statement so as to address it more fully or convincingly. Expand on is a slightly looser term–if you say something interesting in class and the professor asks you to expand on that idea, she wants you to say more, but “more” could mean a lot of things–from explaining the idea in more detail to expressing more thoughts about it at large. Elaborate on is used very similarly, although strictly it refers to expanding something that is by implication underdeveloped by adding details to support or develop an idea, point, statement, theme, or argument. Officials are forever declining to elaborate on the terse comments they give to the press, who just want the scoop.
rSearch and rummage refer to carefully or thoroughly looking for something missing or lost. To search is to carefully move through or look through a place or space to find a person or thing: We searched the amusement park for the missing child; He searched her desk for the letter. Rummage has a narrower range of application and specifies the manner of searching. If you rummage through a suitcase, you move things around or turn them over in order to search. Usually what is rummaged through is a receptacle or a space where things are very close together–a purse, a trash can, cupboards, drawers, an attic, or a wardrobe. If there is only a carton of milk and a package of tofu dogs in the refrigerator, you can’t really rummage through that.
Bitter and acrimonious both describe a person’s nature, speech, or behavior as harsh with anger, resentment, or cynicism. Bitter suggests a deep dissatisfaction or disillusionment that has turned into a resentful or cynical grudge against someone or something–or everything–as if experience had left a bad taste in one’s mouth: her failed dreams had made her bitter. The tone of a bitter debate would be hateful, angry, or sarcastic. An acrimonious debate suggests an angry, even vicious exchange that may also be bitter, but generally is less rooted in personal resentment. However, given the frequent occurrence of acrimonious together with divorce there can be plenty of bitterness signalled by the word acrimonious.