1.the derivation of a word. Synonyms: word origin, word source, derivation, origin.
2.a chronological account of the birth and development of a particular word or element of a word, often delineating its spread from one language to another and its evolving changes in form and meaning. Synonyms: word history, word lore, historical development.
3.the study of historical linguistic change, especially as manifested in individual words.
The character 合 originally comes from from the Chinese mainland, and was much later adopted into Japanese (maybe 1500-1900 years ago.) Pictographically 合 is an inverted mouth 亼 talking to another mouth 口.
Let's start by taking a look at the pieces of the character.
An important radical (part) of this character is a the symbol for mouth/opening.
The meaning of 口 - the mouth / a person / a certain article ( as a cistern, a big jar, etc. ) / the edge or blade of a knife / an opening / a gate ( especially in the Great Wall or city walls ) / a crack
Now let's take a look at the second radical. 亼 - In most contexts represents an upside down mouth - a mouth talking to you. Another meaning of 亼 - to assemble. to gather together
In Chinese 合
to combine / to unite / to gather / to collect / to close / to shut / to suit
In Japanese 合
fit / match / suit / join / combine / unite / coincide / agree