prin·ci·pal parts
noun/ˌprɪnsəpl ˈpɑːts/
/ˌprɪnsəpl ˈpɑːrts/
[plural] (grammar)- the forms of a verb from which all the other forms can be made. In English these are the infinitive (for example swim), the past tense (swam) and the past participle (swum).
（动词）主要部分，主要形式（英语中有动词的不定式、过去时和过去分词）