As interrog. adv. in direct questions: (a) introducing requests for causal information: for what reason?, on account of what?, why?; ~ ever…and wher-fore, wher-fore and ~; (b) introducing rhetorical questions and exclamations, freq. with modal or negative verb phrases: how can it be that (sth. is so)?, why, oh why is it that?;—often implying reproach or protest; also, why (should it not be the case that)?; (c) in elliptical constructions: why is or was that so?, how did that happen?; why?; also used repetitively for emphasis [quot. c1475]; ~ so (not, nought, etc.).

As rel. adv. introducing adj. clauses: (a) with antecedent expressing essentially a causal notion: on account of which, for which; cause (resoun, etc.) ~, the reason that (sth. occurred, sth. is so, etc.), why; also with inf. phrase [quot. c1484]; ~ that; ~ for [see whi-for adv. & conj. (a)]; (b) with antecedent expressing loose or extended causal notions: for which; (c) in elliptical constructions; ensaumple ~, for an example showing why; questioun ~, inquiry as to the reason.

As subordinating conj. introducing adv. clauses: (a) loosely modifying the main clause: as to the reason (that sth. is so);(b) expressing result: such that, so that, for which reason; ~ that; (c) ~ but for-thi, why unless because, for what other reason than that; ~ for [see whi-for adv. & conj. (b)]; (d) in cpd.: ~ so-ever, no matter why (sth. is so), whatever the reason may be that.

As subordinating conj. introducing noun clauses: (a) functioning as subj. or extraposed subj., usu. with inversion of subj. and pred.: for what reason (sth. is, was so, etc.), to what purpose; also with ellipsis of verb in serial construction; also in heading; ~ and wher-fore, hou (wher-of) and ~, etc.; (b) functioning usu. as direct obj. of verbs or verb phrases of knowing, communicating, etc.: the reason that (sth. is so, sb. did sth., etc.), what the reason is that, why; also functioning as appositive to direct obj.; ~ that; ~ and what wise, ~ ne hou, what and ~, etc.; (c) functioning as direct obj. of verbs of asking in indirect questions: for what reason (sb. did sth., sth. occurred, etc.), how it was that, why; ~ so; ~ that; ~ and wher-fore, for what skil and ~, wher-to and ~; (d) functioning usu. as direct obj. in elliptical or truncated constructions; also functioning as subj. [quot. c1385]; (e) functioning as direct obj., in collocation: ~ the cause is, what the cause is, why.

As interjection: well, so, why [cp. wi interj.]: (a) preceding anxious or indignant questions; (b) used with statements, exhortations, demands, etc.