What is the common reading of the word 外海?


外海 has two readings がいかい and そとうみ. What is the difference of the two?
Personally, I am under the impression that がいかい is the common reading because
of its similarity to the word 外国【がいこく】. However, I have encountered situations
(some songs) where そとうみ has been used instead.




The NHK Accent dictionary and the
[大辞林](https://www.weblio.jp/content/%E5%A4%96%E6%B5%B7) include both がいかい and
そとうみ readings as valid for this term.

The デジタル大辞泉 lists the first definition of _kaigai_ and _sotoumi_ as synonyms
for a sea that is not bound by the continent, or to the open sea that is not
close to the continent. However, the second definition of _kaigai_ , which is
more metaphorical, means foreign lands, and I couldn´t find this connotation
in the definitions of _sotoumi_. Here are the definitions for
[がいかい](https://dictionary.goo.ne.jp/word/%E5%A4%96%E6%B5%B7_%28%E3%81%8C%E3%81%84%E3%81%8B%E3%81%84%29/#jn-35413)
and
[そとうみ](https://dictionary.goo.ne.jp/word/%E5%A4%96%E6%B5%B7_%28%E3%81%9D%E3%81%A8%E3%81%86%E3%81%BF%29/#jn-131002).

Additionally, there is the Buddhist term
[げかい](https://dictionary.goo.ne.jp/word/%E5%A4%96%E6%B5%B7_%28%E3%81%92%E3%81%8B%E3%81%84%29/#jn-67403)
that uses the same kanji.

Also, there is at least one person name with these kanji
([とのがい](https://www.weblio.jp/content/%E3%81%A8%E3%81%AE%E3%81%8C%E3%81%84)).

