The words which are not derived or developed from other words are called primary words. Primary words are the original words in a language.

Compound words
Some words are formed by joining two or more simple words. These words are called compound words. Examples are: sunlight, however, kindness, undertake etc.

Primary derivatives

These are words formed by making some changes to the spelling of a simple word.

Examples are given below:
Bond is a primary derivative formed by making some internal changes the word bind. Similarly, breach is a primary derivative formed by making some changes to the simple word break.

Note that past tense forms which are made by making some internal changes to primary verbs are not usually considered as derivatives.

Secondary derivatives
These are formed by making an addition to the beginning or the end of a word. Examples are: unhappy and kindness.

Note that the addition made to the beginning of a word is called a prefix whereas an addition made to the end is called a suffix.

Compound words
Most compound words are nouns, verbs or adjectives.

Compound nouns
Compound nouns are usually formed by the following combinations.

Noun + noun

Examples are: railway, postman, shoemaker, horsepower, windmill, teaspoon, airman, manservant, screwdriver etc.

Armchair (arm + chair)
Sunlight (sun + light)

Adjective + noun

Examples are: shorthand, sweetheart, blackboard, stronghold, halfpenny etc.

Verb + noun

Examples are: spendthrift, makeshift, breakfast, daredevil, pickpocket, hangman etc.

Gerund + noun

Examples are: drawing room, bloating paper, stepping-stone, walking-stick, looking-glass etc.

Adverb/preposition + noun

Examples are: Outlaw, afterthought, foresight, bypass, downfall, afternoon

Verb + adverb

Examples are: drawback, send-off, die-hard, go-between etc.

Adverb + verb

Examples are: outset, upkeep, outcry, income, outcome etc.

Compound adjectives are formed from:

Noun + adjective

Examples are: blood-red, sky-blue, snow-white, skin-deep, pitch-dark, worldwide, lifelong, homesick, seasick etc.

Noun + participle

Examples are: heart-rending, ear-piercing, heartbroken, bedridden and lovelorn

Adjective + adjective

Examples are: red-hot, lukewarm etc.

Adverb + participle

Examples are: long-suffering, everlasting, outspoken, down-hearted, thorough-bred, inborn etc.

Compound verbs are formed from

Noun + verb

Examples are: earmark, browbeat, backbite, typewrite etc.

Adjective + verb

Examples are: safeguard, fulfill, whitewash etc.

Adverb + verb

Examples are: overtake, undertake, undergo, outbid, upset, outdo etc.