内線|ないせんnaisen[0]heiban (flat)

1. nounphone extension; indoor wiring; inner line
   内線ないせん２１４に出でる人ひとなら誰だれでも構かまいません。↗

   I'll speak to anyone at extension 214.

• RelatedホームテレホンNeutralA loanword for a home telephone device or system, whose very name suggests home use; 「内線」 broadly covers extensions and lines within a building.
• Related親子電話おやこでんわNeutralPhones sharing a single line as a parent-and-child set, typically home equipment; 「内線」 is the line or extension linking phones within a building.
• Antonym外線がいせんNeutralThe line connecting to the outside, the opposite of 「内線」, which links phones within a building; extensions can also call out through the outside line.

Use 「内線」 for phone extensions within a company or building, as in 「内線123番」; lines going outside are 「外線」, and home parent-child phone sets are 「親子電話」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 同おなじ建物たてものの中なかの電話機でんわきを結むすぶ通信つうしん回線かいせん。
2. 建物たてもの内部ないぶに設置せっちされた電気でんき配線はいせん。