綻びる

1. Origins, structure, and basic meaning

• Structure: 綻びる (ほころびる) adds okurigana びる to coming apart 綻, forming an intransitive verb.
• Basic usage: It describes a seam opening and, figuratively, a face breaking into a smile.

2. Common pitfalls and similar expressions

• A seam and a smile
  • Clothing gives the literal sense “come apart,” while 顔が綻びる depicts facial tension opening into happiness.