プログレッシブ和英中辞典(第4版)の解説
ほんすじ【本筋】
❶〔話の主題目〕
本筋に入る
「take up [move on to] 「the main topic [the central theme] ((of one's talk))
本筋を外れる
digress from one's [the] main subject／get off the subject ((of one's talk))
話を本筋に戻すと…
Getting back to our main subject....
❷〔正当な筋道〕
まず彼に相談するのが本筋でしょう
The proper thing would be to consult him first.