What are the differences between them?
From dictionary.com:
fun Pronunciation Key (fn)
n.
A source of enjoyment, amusement, or pleasure.
Enjoyment; amusement: have fun at the beach.
Playful, often noisy, activity.
intr.v. Informal funned, fun·ning, funs
To behave playfully; joke.
adj. Informal
Enjoyable; amusing: ?You're a real fun guy? (Margaret Truman).
Idiom:
for/in fun
As a joke; playfully.
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[Possibly from fon, to make a fool of, from Middle English fonnen, to fool, possibly from fonne, fool.]
Usage Note: The use of fun as an attributive adjective, as in a fun time, a fun place, probably originated in a playful reanalysis of the use of the word in sentences such as It is fun to ski, where fun has the syntactic function of adjectives such as amusing or enjoyable. The usage became popular in the 1950s and 1960s, though there is some evidence to suggest that it has 19th-century antecedents, but it can still raise eyebrows among traditionalists. The day may come when this usage is entirely unremarkable, but writers may want to avoid it in more formal contexts.
joy Pronunciation Key (joi)
n.
Intense and especially ecstatic or exultant happiness.
The expression or manifestation of such feeling.
A source or an object of pleasure or satisfaction: their only child, their pride and joy.
v. joyed, joy·ing, joys
v. intr.
To take great pleasure; rejoice.
v. tr. Archaic
To fill with ecstatic happiness, pleasure, or satisfaction.
To enjoy.
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[Middle English joie, from Old French, from Latin gaudia, pl. of gaudium, joy, from gaudre, to rejoice. See gu- in Indo-European Roots.]
pleas·ure Pronunciation Key (plzhr)
n.
The state or feeling of being pleased or gratified.
A source of enjoyment or delight: The graceful skaters were a pleasure to watch.
Amusement, diversion, or worldly enjoyment: ?Pleasure... is a safer guide than either right or duty? (Samuel Butler).
Sensual gratification or indulgence.
One's preference or wish: What is your pleasure?
v. pleas·ured, pleas·ur·ing, pleas·ures
v. tr.
To give pleasure or enjoyment to; gratify: Our host pleasured us with his company.
v. intr.
To take pleasure; delight: The hiker paused, pleasuring in the sounds of the forest.
To go in search of pleasure or enjoyment.
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[Middle English, from Old French plaisir, from plaisir, to please. See please.]
From dictionary.com:
fun Pronunciation Key (fn)
n.
A source of enjoyment, amusement, or pleasure.
Enjoyment; amusement: have fun at the beach.
Playful, often noisy, activity.
intr.v. Informal funned, fun·ning, funs
To behave playfully; joke.
adj. Informal
Enjoyable; amusing: ?You're a real fun guy? (Margaret Truman).
Idiom:
for/in fun
As a joke; playfully.
--------------------------------------------------------------------------------
[Possibly from fon, to make a fool of, from Middle English fonnen, to fool, possibly from fonne, fool.]
Usage Note: The use of fun as an attributive adjective, as in a fun time, a fun place, probably originated in a playful reanalysis of the use of the word in sentences such as It is fun to ski, where fun has the syntactic function of adjectives such as amusing or enjoyable. The usage became popular in the 1950s and 1960s, though there is some evidence to suggest that it has 19th-century antecedents, but it can still raise eyebrows among traditionalists. The day may come when this usage is entirely unremarkable, but writers may want to avoid it in more formal contexts.
joy Pronunciation Key (joi)
n.
Intense and especially ecstatic or exultant happiness.
The expression or manifestation of such feeling.
A source or an object of pleasure or satisfaction: their only child, their pride and joy.
v. joyed, joy·ing, joys
v. intr.
To take great pleasure; rejoice.
v. tr. Archaic
To fill with ecstatic happiness, pleasure, or satisfaction.
To enjoy.
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[Middle English joie, from Old French, from Latin gaudia, pl. of gaudium, joy, from gaudre, to rejoice. See gu- in Indo-European Roots.]
pleas·ure Pronunciation Key (plzhr)
n.
The state or feeling of being pleased or gratified.
A source of enjoyment or delight: The graceful skaters were a pleasure to watch.
Amusement, diversion, or worldly enjoyment: ?Pleasure... is a safer guide than either right or duty? (Samuel Butler).
Sensual gratification or indulgence.
One's preference or wish: What is your pleasure?
v. pleas·ured, pleas·ur·ing, pleas·ures
v. tr.
To give pleasure or enjoyment to; gratify: Our host pleasured us with his company.
v. intr.
To take pleasure; delight: The hiker paused, pleasuring in the sounds of the forest.
To go in search of pleasure or enjoyment.
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[Middle English, from Old French plaisir, from plaisir, to please. See please.]