SYNONYM, ANTONYM AND POLYSEMY

SYNONYMS
Synonyms are different words which have the same meaning, or almost the same meaning.

The words stones and rocks are synonyms.

Synonyms can be nouns, verbs, adverbs or adjectives, as long as both are the same part of speech.

For example:
- chair and seat (nouns)
- go and leave (verbs)
- quickly and rapidly (adverbs)
- long and extended (adjectives)

Synonyms need not be single words, as in war and armed conflict.

Here are more synonyms:

- tremendous and remarkable
- cat and feline
- baby and infant
- sick and ill
- quickly and speedily

A word can have more than one synonym depending on which meaning you use for the word.
For example:
- expired could have the synonym no longer fresh, if you mean milk that's past its sale date.
- expired could have the synonym dead, if you mean no longer alive.
  
ANTONYMS 
Antonyms are words which have opposite meanings.

The words hot and cold are antonyms. So are up and down, and short and tall.

A word can have more than one antonym, depending on which meaning you use for the word.
For example:
- short could have the antonym tall if you are referring to a person's height.
- short could have the antonym long if you are referring to to the length of something.

In many languages, including English, you can sometimes make antonyms by adding a prefix:
- real and unreal are antonyms
- flexible and inflexible are antonyms
However, English is well known for its exceptions to the rules, so you have to watch out for words like flammable and inflammable, where this doesn't work ... they're synonyms!

There are actually four types of antonyms:

• Gradable antonyms are opposites at either end of the spectrum, as in slow and fast.
• Complementary antonyms are absolute opposites, like mortal and immortal.
• Relational antonyms are opposites where one word describes a relationship between two objects, and the other word describes the same relationship when the two objects are reversed.
     For example, parent and child, teacher and student, or buy and sell.
• Auto-antonyms are the same two words that mean the opposite.
     For example, fast (moving quickly) and fast (stuck in place).

 POLYSEMY
Polysemy  is an intimidating compound noun for a basic language feature. This happens when a lexeme acquires a wider range of meanings.
For example, paper comes from Greek papyrus. Originally it referred to writing material made from the papyrus reeds of the Nile, later to other writing materials, and now to things such as government documents, scientific reports, family archives or newspapers.

More Examples

Mole

1. a small burrowing mammal
2. consequently, there are several different entities called moles (see the Mole disambiguation page). Although these refer to different things, their names derive from 1. :e.g. A Mole burrows for information hoping to go undetected.

Bank

1. a financial institution
2. the building where a financial institution offers services
3. a synonym for 'rely upon' (e.g. "I'm your friend, you can bank on me"). It is different, but related, as it derives from the theme of security initiated by 1

However: a river bank is a homonym to 1 and 2, as they do not share etymologies. It is a completely different meaning. River bed, though, is polysemous with the beds on which people sleep.

Book

1. a bound collection of pages
2. a text reproduced and distributed (thus, someone who has read the same text on a computer has read the same book as someone who had the actual paper volume)
3. to make an action or event a matter of record (e.g. "Unable to book a hotel room, a man sneaked into a nearby private residence where police arrested him and later booked him for unlawful entry.")

Milk

The verb milk (e.g. "he's milking it for all he can get") derives from the process of obtaining milk.

Present

1. right now, the current moment
2. a gift
3. to show or display (e.g. "Michael was next to present")
4. to be physically somewhere (e.g. "Stephen was present at the meeting")

Wood

1. a piece of a tree
2. a geographical area with many trees
3. an erection

Crane

1. a bird
2. a type of construction equipment

http://www.worsleyschool.net/socialarts/synonyms/page.html 
http://www.teachit.co.uk/armoore/lang/semantics.htm#14
http://en.wikipedia.org/wiki/Polysemy