What is a word for the most basic form of a term? [closed]

The English language contains very descriptive and "involved" words, I was wondering what we would call the opposite of those.

For example, words like "push" or "hot" can't be simplified further without losing their meaning. What do you call a term in its most basic form?

Example:

scorching may imply a very high level of heat or hot.
heat or hot are basic terms that don't imply any enhancement (How hot, how much heat).

Solution 1:

essence: the intrinsic or indispensable properties that serve to characterize or identify something; the crucial element. in essence: by nature

From Latin esse, to be.

Synonyms include *substance, gist, core, sum, marrow, heart, center, hypostasis (essential nature or underlying reality), haecceity, quiddity (the essence that makes something the kind of thing it is and makes it different from any other) quintessence (the purest and most concentrated essence of something), stuff

Solution 2:

Irreducible concepts are axiomatic.

An axiomatic concept is the identification of a primary fact of reality, which cannot be analyzed, i.e., reduced to other facts or broken into component parts.

Solution 3:

germ

It's sort of customary to call such a thing the germ of an idea.

http://www.oxforddictionaries.com/definition/english/germ

(scroll down to see 22 "the germ of a brilliant idea")

Solution 4:

I don't think there is a special word in reference to words. However, I think atomic is what I would use to describe the concept of a word that could not be broken down any further:

of or forming a single irreducible unit or component in a larger system. Google definition