Japanese words phenomenon

I am searching for the name of a phenomenon I noticed in japanese.
An example for a phenomenon is 連濁
The phenomenon I noticed is words that are created by two similar kanji, variants of one another or kanji that can be used to create the same words.
喪う often written as 失う.
When you take this two kanji that can be used to create the same verb you get a word 喪失
河 and 川 are both river. when those two variants are combined we get 河川
停 and 止 can be used to write とまる and とめる (although the latter is more common). When combine 停止
温 and 暖 are both warm(used to describe different things) when combined 温暖
How is this thing called?

熟語の構成 - there are categories of kanji compounds (熟語) by how they are constructed(構成), the categories don't have short names as far as I know but recognising these is tested in tested in some kanji tests (e.g. Kanken)

1. Two kanji with similar meanings, e.g. 岩石
2. Two kanji with opposite/opposing meanings, e.g. 強弱
3. The first kanji modifies the second, like an adjective or similar - 美人 = 美しい人
４．The first kanji represents a verb and the second is the object
握手 = 手を握る 着席 = 席に着く

Then there are ones with negating prefixes like 無、非 etc which are similar to un- in English.