Sub-

can someone explain me please what is it subconcept?

I took it from the sentece: Although the four conservation principles initially appear simple, they contain subconcepts.....

If you take the view that the word should be 'sub-concepts' then all becomes clear. This is an example of the sloppy use of the English language leading to unnecessary, and unintended, confusion.

The subject title that you gave to your posting - 'word that I can't finf in the dictionary' - is also sloppy usage of the language - capitalizing 'i' and changing the spelling of 'finf' to 'find' adds considerable clarity to your question.

I also notice that another word you use - 'sentece' - does not appear in the dictionary.

And a merry Christmas to you.

Make that: Merry Christmas.

And further more, the word was "subconcept" at all the Web sites I visited.

Make that "furthermore." Now, about "sub-": The general rule for hyphenation after a prefix is don't. "Sub" is a complete word when it's slang for submarine. It's not a word when it joins with "concept" to form a compound: it's a prefix. So "subconcept" is correct.

Exceptions: Hyphenate to avoid a double vowel, as in "anti-intellectual" (but some exceptions to this exception are accepted, as "preeminent" and "cooperate"). Hyphenate if the second element is capitalized, as in "pre-Socratic."

Just a few examples from an online dictionary - can't all be wrong.

1. sub-zero
2. sub-underwrite
3. sub-standard
4. sub-Saharan
5. sub rosa
6. sub-post office
7. sub-postmistress
8. sub-postmaster
9. sub-plot
10. sub-orbital
11. sub-nuclear
12. sub-machine gun
13. Sub-Lt.
14. sub-lessor
15. sub-lessee
16. sub-clause
17. sub-breed
18. Sub-Boreal
19. sub-basement
20. Sub-Atlantic

Quite right--they aren't all wrong. For instance, "sub-Saharan" and "sub-Atlantic" are correct because "subSaharan" and "subAtlantic" would look terrible. In "sub rosa," the first element is a (Latin) word, not a prefix. However, the forms "subzero" and "subplot" are standard, unlike their hyphenated versions. Not everything that's on-line is authoritative.

Presumably you accept that the OED has some credibility in these matters; or perhaps you don't?