noun
fishing-net weight; sinker
A weight attached to a fishing net to make it sink. The spelling 錘 is standard; 沈子 is also used.
漁師は網に錘を付けて沈めた。
The fisherman attached weights to the net and sank it.
この錘は鉛でできている。
This sinker is made of lead.
おもり is a general weight used for various purposes, while 錘 (いわ) specifically refers to a fishing-net weight.
The reading いわ is likely related to 岩 (rock), as stones were traditionally used as weights. The kanji 錘 means 'weight' or 'spindle'.