An expression that adds little information

Question

There is a family of expressions called oxymorons which contain contradicting meanings. What about expressions that add little meaning like "fatally injured"? What are these expressions called?

Answer 1

These are known as tautologies or tautologous expressions.

Some examples from the Guardian Style Guide:

Aum Shinrikyo
means Supreme Truth sect, but note that the "aum" means sect, so to talk about the "Aum sect" or "Aum cult" is tautologous

affidavit
a written declaration made on oath, so "sworn affidavit" is tautologous.

Eid al-Adha
(Festival of Sacrifice) Muslim festival laid down in Islamic law, celebrates the end of the hajj. Note that eid means festival, so it is tautologous to describe it as the “Eid festival

gambit
an opening strategy that involves some sacrifice or concession; so to talk of an opening gambit is tautologous — an opening ploy might be better

regalia
plural, of royalty; “royal regalia” is tautologous

As a side note, tautologies are often found in place names, my favourite is The La Brea Tar Pits, meaning The The Tar Tar Pits.

Answer 2

I've found the word I was looking for. It's pleonasm:

http://en.wiktionary.org/wiki/pleonasm

pleonasm (countable and uncountable; plural pleonasms) (uncountable, rhetoric) Redundancy in wording.  [quotations ▼] (countable) A phrase involving pleonasm, that is, a phrase in which one or more words are redundant as their meaning is expressed elsewhere in the phrase. "The two of them are both the same" is a pleonasm (as the word "both" is redundant), as is "killed dead".

Some better examples:

• "Could you repeat that again?"
• "It's a really new innovation"

In the same genre there is also redundancies and tautologies.