noun (used with a plural verb) Grammar.
a set of inflected forms of a form class from which all the other inflected forms can be derived, as sing, sang, sung; smoke, smoked.
Origin of principal parts
First recorded in 1865–70
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
grammar the main inflected forms of a verb, from which all other inflections may be deduced. In English they are generally considered to consist of the third person present singular, present participle, past tense, and past participle
the sides and interior angles of a triangle
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012