principal part

Calque of Late Latin principālis pars

principal part (plural principal parts)

1. (grammar, usually in the plural) Any of the forms of a word which contain its stem(s) in the simplest form, or such a form that, when taken with all the other principal parts, allows the entire paradigm to be derived.
2. (mathematics) A polynomial approximation of a power series, made up of monomials whose indices lie in the Newton diagram of the power series and which occur with the same coefficients as in the original power series.
3. (mathematics) The portion of a Laurent series that has negative exponents.
4. Used other than with a figurative or idiomatic meaning: see principal,‎ part.

• In Latin grammar: the two principal parts of a noun are the singular nominative and the singular genitive; the three of an adjective are the masculine, the feminine, and the neuter singular nominatives; and the four of a verb are the first-person singular present active indicative, the 1st-pers. sg. perfect act. ind., the pres. act. infinitive, and the supine (or, in the case of deponent verbs, the three are the 1st-pers. sg. pres. act. ind., the pres. act. inf., and the perf. act. participle).
• In the grammars of most Germanic languages: the three principal parts of verbs are the present infinitive, the first-person singular imperfect indicative, and the passive participle.
• In English grammar: the two principal parts of a noun are the singular and the plural; the three of an adjective are the positive, the comparative, and the superlative; and the three of a verb are the infinitive, the simple past, and the past participle.

• A New English Dictionary on Historical Principles (1st ed.), volume VII (O–P, ed. James Augustus Henry Murray, 1909), § 2 (P), page 499/1 s.v. “Part, sb. (adv.)”, sense 19.b

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