Two characters words are all compound words. There are different ways to coin compound words
One way to coin compound word is to combine two characters that share a similar meaning to make it specific
Most single character words contain multiple meanings thus make them too general for expressing a more specific meaning.
Example (adj + adj) :
沉 can mean 'sing' or 'heavy'
To make a specific term, we add one more character to it to clarify the meaning
没 also have the meaning of 'sink', That make '沉没' specifically mean 'sink'
重 also have the meaning of 'heavy' That make, '沉重' specifically mean 'heavy'
Example (verb + verb) :
攻 means 'attack' but it also contains the meaning of: study; specialize in; work at
擊 mainly mean 'hit' but it also contains the meaning of: 'attack'
攻擊 is a specific term for 'attack'
Question: Is there a name for 2-character "in-between" words in which both characters are abbreviations for individual 2-character words?
攻擊 are not abbreviations for 攻打 and 打擊
攻擊, 攻打 and 打擊 are all compound words that happen to share one component (攻擊 and 攻打 share 攻; 攻打 and 打擊 share 打)
Example from this post 认识 vs 知道 based on glyph origins
見識: experience(v) = (see + know) *'to see to know'
見識: experience(n)= (see + knowledge) knowledge from what you had seen
學識: knowledge; acquirements (n) = (learn/study + know) knowledge from what you had studied
常識: common sense; general knowledge(n) = (common + knowledge) knowledge that is common
They are all compound words that share the 識 component
It doesn't mean 見識 are abbreviations of 眼見/看見 and 認識/知識
It doesn't mean 常識 are abbreviations of 平常/通常 and 認識/知識