セビロ is usually written in katagana and comes from the word Saville Row, a street in Mayfair London known mainly for tailoring suits.
背広 is ateji (kanji used for their phonetic readings)
As a Japanese speaker, people don't usually refer to a suit as せびろ。They usually refer it to be a suit written in katagana
I lived in Japan for 7 years and I never heard the word せびろ even once that I can recall.
Is this interchangeable with スーツ or do they mean slightly different things?
Suits may mean the whole ensemble whereas 背広 may only infer the jacket.
Does DL pronounce it like せびの instead of せびろ or is that just me?
The Japanese "r" sound is actually a sound between an "r" and an "l" that your ear might not be used to yet, which is why it sounds like an "n" to you.
I always understood sebiro to mean business suit so I used that instead of just suit. It was counted wrong.
From 辞書, the word 背広(せびろ) is business suit. And suit is スイツ.
スイツ is wrong. It's スーツ
Fat guy in little coat.
Exactly what I came to the comments section for Tommy!