便|びんbin[1]atamadaka (head-high)

1. noun, noun (suffix)flight (e.g. airline flight); trip (e.g. train trip); sailing (e.g. ferry voyage); service
   ちょっとした事故じこが原因げんいんで、２、３便びんに遅おくれが出でた。↗

   A couple of flights were delayed on account of a minor accident.
2. noun, noun (suffix)mail; post; letter
3. noun, noun (suffix)opportunity; chance

• Synonym手紙てがみNeutralThe everyday, most common word for a letter itself. 「便」 centers on scheduled runs such as flights and mail, and often works as a suffix, as in 「航空便」.
• Synonym文ふみWrittenA literary, old-fashioned word for a letter, as in 「恋文」; still used in modern prose. 「便」 leans toward transport and mail delivery.
• Synonym便りたよりNeutralNews or tidings from someone, often a letter, with a warm feel. 「便」 stresses flights and mail runs rather than the message itself.
• Antonym不便ふべんNeutralRead ふべん: inconvenience, being unhandy. It is the opposite of 「便」 only in the convenience sense, with nothing to do with flights or mail.

Use 「便」 for flights, scheduled runs and mail, as in 「次の便」 or 「宅配便」. For a letter say 「手紙」; for news from someone, 「便り」; 「文」 is a literary alternative. 「不便」 opposes it only in the convenience sense.

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

1. （ビン）人にん・荷物にもつ・手紙てがみなどを運はこぶこと。また、その手段しゅだん。
2. （ビン）都合つごうのいい機会きかい。