脱線(だっせん)

だっせん
noun
derailment, digression
transportation
1. derailment
When a train or vehicle leaves the tracks.
電車(でんしゃ)が脱線(だっせん)した。
The train derailed.
脱線(だっせん)事故(じこ)で遅延(ちえん)が発生(はっせい)した。
A derailment accident caused delays.
2. digression, going off topic
Straying from the main subject in a conversation or discussion.
話(はなし)が脱線(だっせん)してしまった。
The conversation went off topic.
すみません、話(はなし)が脱線(だっせん)しましたが、本題(ほんだい)に戻(もど)りましょう。
Sorry, I got off topic, but let's get back to the main subject.
先生(せんせい)の授業(じゅぎょう)はよく脱線(だっせん)するが、その話(はなし)が面白(おもしろ)い。
The teacher often goes off topic in class, but those digressions are interesting.

脱線(だっせん) has both literal (train derailment) and figurative (going off topic) meanings.

Common expressions

Usage

The figurative use is very common in casual conversation when someone strays from the main topic.

Related Words

Related: 逸脱(いつだつ) (deviation; departure)
Compare: 脇道(わきみち)にそれる (to go off on a tangent)
general
Added 2026.1.14 9:33 · Revised 2026.9.2 13:01
04500/04514_dassen