tauto-, taut- +

(Greek: same)

redundancies, tautologies, and pleonasms
tautegorical
Expressing the same thing with different words; opposed to allegorical.
tautochrome
Apparently a misspelling of tautochrone.
tautochromism
Apparently a misspelling of tautochronism.
tautochrone
That curve upon which a particle moving under the action of gravity (or any given force) will reach the lowest (or some fixed) point in the same time, from whatever point it starts.

A tautochrone or isochrone curve is the curve for which the time taken by a frictionless particle sliding down it under uniform gravity to its lowest point is independent of its starting point. The curve is a cycloid, and the time is equal to π times the square root of the radius over the acceleration of gravity.

tautochronism
Occupying the same time; pertaining to, or having the properties of, a tautochrone.
tautochronous
Having the character of a tautochrone; occupying the same time, isochronous.
tautologia
The repetition of the same idea in different words, but (often) in a way that is wearisome or unnecessary. This should not be confused with the logical notion of tautology.
tautologic
Repetition of the same sense in different words.
tautological
A reference to, characterized by, involving, or using tautology; that is, repeating the same word, or the same notion in different words.
Tautologies and Pleonasms
Tautologous expressions are often used in legal documents for clarification of meaning; such as, "will and testament" and "breaking and entering".

This practice may have been a result of expressing English documents with a mixture of Anglo-Saxon and French, or Latin terms.

When early writers weren't sure if both designations had the same meaning, or that others might not have a clear understanding of the French or Latin, they apparently included terms from both the Anglo-Saxon and the "foreign"; words side by side, just to be sure others understood what was meant. This is according to David Crystal in The Cambridge Encyclopedia of Language.

Pleonasms are the opposites (antonyms) of oxymora. A pleonasm consists of two concepts (usually two words) that are redundant. What does "redundant" mean? Well, how about "more than enough; overabundant; excessive; and superfluous"?

Still having a problem understanding what pleonasm means? Some pleonastic expressions are also known as tautologies. Tautology means, "needless repetition of an idea in a different word, phrase, or sentence; redundancy; pleonasm". All right, what about pleonasm? Well, it means, "the use of more words than are necessary for the expression of an idea; redundancy".

So it is that we go around in circles: pleonasm means tautology, which means redundancy, which means pleonasm, which means tautology, ad infinitum.

tautologism
1. The use of tautology.
2. A tautology.
tautologist
Someone who uses tautological words or phrases.
tautologize, tautologizes; tautologized; tautologizing (verbs
1. To repeat the same thing in the same or with different words.
2. Using tautology.
tautologous
1. Repeating the same thing in different words; tautological.
2. Involving or containing rhetorical tautology; redundant.
3. True by virtue of its logical form alone.

Inter-related cross references, directly or indirectly, involving word units dealing with "equal, identical, same, similar": auto-; emul-; equ-, equi-; homeo-; homo-; iso-; pari-; peer; rhomb-; syn-.