Definition of simple adjective from the Oxford Advanced Learner's Dictionary

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simple

adjective
ˈsɪmpl
 
; ˈsɪmpl
 
simpler, simplest
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You can also use more simple and most simple.
 
 

easy

1 not complicated; easy to understand or do
Synonym
easy
a simple solutionThe answer is really quite simple.This machine is very simple to use.We lost because we played badly. It's as simple as that.Give the necessary information but keep it simple.
 

basic/plain

2 basic or plain without anything extra or unnecessarysimple but elegant clothesWe had a simple meal of soup and bread.The accommodation is simple but spacious.simple pleasures, like reading and walking
Opposite
fancy
 

for emphasis

3 used before a noun to emphasize that it is exactly that and nothing elseNobody wanted to believe the simple truth.It was a matter of simple survival.It's nothing to worry about—just a simple headache.I had to do it for the simple reason that(= because) I couldn't trust anyone else.
 

with few parts

4 [usually before noun] consisting of only a few parts; not complicated in structuresimple forms of life, for example amoebasa simple machine (grammar) a simple sentence(= one with only one verb)
 

ordinary

5 [only before noun] (of a person) ordinary; not specialI'm a simple country girl.
 

not intelligent

6 [not usually before noun] (of a person) not very intelligent; not mentally normalHe's not mad—just a little simple.
 

grammar

7 used to describe the present or past tense of a verb that is formed without using an auxiliary verb, as in She loves him (= the simple present tense) or He arrived late (= the simple past tense)
see also simply
Idioms
see
pure and simple at pure
Usage noteUsage note: plainsimple stark bare unequivocalThese words all describe statements, often about something unpleasant, that are very clear, not trying to hide anything, and not using more words than necessary.plain used for talking about a fact that other people may not like to hear; honest and direct in way that other people may not like:The plain fact is that nobody really knows.simple [only before noun] used for talking about a fact that other people may not like to hear; very obvious and not complicated by anything else:The simple truth is that we just can't afford it.plain or simple?When it is being used to emphasize facts that other people may not like to hear, plain is usually used in the expression the plain fact/truth is that…Simple can be used in this way too, but it can also be used in a wider variety of structures and collocations (such as reason and matter):The problem was due to the simple fact that… The problem was due to the plain fact that… for the plain reason that… It's a plain matter of… Expressions with simple often suggest impatience with other people's behaviour.stark (rather formal) used for describing an unpleasant fact or difference that is very obvious:The stark truth is that there is not enough money left. The simple/plain truth may be something that some people do not want to hear, but it may be good for them to hear it anyway. The stark truth is something particularly unpleasant and has no good side to it at all.bare [only before noun] the most basic or simple, with nothing extra:She gave me only the bare facts of the case.unequivocal (formal) expressing your opinion or intention very clearly and firmly:The reply was an unequivocal ‘no’.the plain/simple/stark/bare/unequivocal trutha(n) plain/simple/stark/bare/unequivocal fact/statementa(n) plain/simple/unequivocal answer