Item, detail, particular are comparable when meaning one of the things, either separate and distinct or considered so, which constitute a whole.
Item applies mainly to each thing that is put down in a list (as of things needed, things to be done, or things to be seen) or in an account, a record, or an inventory; sometimes the term applies to the actual thing as apart from the list.
Detail (see also PART ) applies to each separate thing which enters into the building or construction of some such thing as a house, a painting, or a narrative or enters into such an activity as the performance of a task or job, the pursuit of a career, or the living of a life; often, in this sense, detail is contrasted with structure, outline, design, or plan.
Often the singular form in this sense is used as a collective noun.
Particular may imply a relation to something general or universal, but more often it implies a relation to a whole and stresses that relationship more than item or detail; in this sense particular emphasizes the smallness and the singleness and concreteness of each item or detail; thus, in law, a bill of particulars is a statement of the items of a plaintiff's claim or a defendant's counterclaim.