noun
General term for rope or cord; often used in technical or formal contexts, such as in engineering or nautical settings.
この索はとても丈夫だ。
This rope is very strong.
ロープ is the common loanword for rope, used in everyday contexts. 索 is more formal or technical.
The kanji 索 originally depicts a rope or cord. The reading さく is the on'yomi, and the word is used in formal or technical contexts.