Learn English – the difference between amid and amidst

Merriam-Webster's Dictionary of Synonyms (1984) includes explicate and expound—together with elucidate, interpret, and construe—in a group under the heading word explain. Here is its treatment of expound and explicate:

Expound implies careful, elaborate, often learned setting forth of a subject in order to explain it (as in a lecture, a book, or a treatise) {a clergyman expounding a biblical text} {expound a point of law} {Sir A. Eddington in two masterly chapters ... expounds the law of gravitation—Alexander} {expound the duties of the citizen} Explicate, a somewhat learned term, adds to expound the idea of development or detailed analysis {the mind of a doctor of the Church who could ... explicate the meaning of a dogma—T.S. Eliot}

An earlier edition of Webster's Dictionary of Synonyms (1942) has an identical treatment of the two words, except that also says that explicate means "literally, to unfold."

S.I. Hayakawa, Choose the Right Word (1968), on the other hand, groups explicate with elucidate, explain, and interpret under the heading word clarify, but doesn't address expound at all. Here is Hayakawa's commentary on explicate:

Explicate is more restricted and specific in use than the foregoing [clarify and elucidate]. It refers to a point-by-point discussion of a complex matter, especially as in the paraphrase and analysis of a literary text: asking each student to explicate the difficult poem; popular books that attempt to explicate Einstein's theories.

Putting the two discussions together, I would surmise that, although both terms imply a carefully developed (and usually, scholarly) investigation and presentation of a subject, explicate has a stronger sense of a line-by-line or point-by-point analysis of the subject, whereas expound is just as learned but perhaps a bit more general in its treatment and more inclined to elaborate on the implications of the broader subject.

They can often be used interchangeably. A 'dose' is a countable unit of it (1 spoonfuls, etc). The uncountable 'dosage' is what the doctor prescribes.

The following extract from MedLinguistic explains the difference:

• Despite repeated emphasis upon the distinction between dose and dosage, these two terms continue to baffle us. As we’ve often been told, dose refers to a specified amount of medication taken at one time.

• In the preferred use of dosage, however, the term refers to the administering of a specific amount, number, and frequency of doses over a specified period of time. Dosage implies duration: a “dosage regimen” is a treatment plan for administering a drug over a period of time.