n. 1
State of mind; mood.
n. 2
Anger; a fit of anger.
When I heard about it I got myself into a terrible temper.
v. 1
To moderate or control.
Temper your language around children.
v. 2
To strengthen or toughen a material, especially metal, by heat treatment; anneal.

Related words

Word family: temperament temperance temperate temperer tempering
Phrases: lose one's temper short temper bad temper temper tantrum temper foam

Forms

Plural: tempers → moods, humors, composures, spirits…
Past participle: tempered
e.g. tempered → moderated, abated, mollified, seasoned…

Temper or Anger?

Temper used alone in the sense of anger is colloquial, tho we may correctly say a hot temper, a fiery temper, etc.

J. C. Fernald, English Synonyms and Antonyms (1914)

Use in printed books, per decade from 1850 to 2019.

3 letters: fit¹
4 letters: cool¹, tone¹, mood¹, rage¹
5 letters: frame¹, anger², relax², humor², grain¹, adapt², blunt¹, pique¹, abate², allay²
6 letters: season², nature², spirit², adjust², humour², modify³, harden², soften², soothe¹, subdue², animus³, pacify³, anneal²
7 letters: quality³, passion², spirits², qualify³, appease², assuage², mollify³, chasten²
8 letters: moderate³, mitigate³, additive³, restrain², hardness², calmness², palliate, attemper, attempre
9 letters: character³, toughness², temperate², composure³, normalize³, normalise, surliness
10 letters: irritation⁴, equanimity⁵
11 letters: disposition⁴, temperament³, peevishness, biliousness, pettishness
12 letters: irritability⁶, snappishness

The small number after each word is its number of syllables (anger² = 2 syllables).