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

Oxford3000

old

adjective
əʊld
 
; oʊld
 
older, oldest
 
 

age

1 be… years, months, etc. old of a particular ageThe baby was only a few hours old.In those days most people left school when they were only fifteen years old.At thirty years old, he was already earning £40000 a year.two fourteen-year-old boysa class for five-year-olds (= children who are five)I didn't think she was old enough for the responsibility.How old is this building?He's the oldest player in the team.She's much older than me.
 

not young

2 having lived for a long time; no longer youngto get/grow oldThe old man lay propped up on cushions.She was a woman grown old before her time(= who looked older than she was).
Opposite
young
3 the old noun [plural] old peopleThe old feel the cold more than the young.
 

not new

4 having existed or been used for a long timeold habitsHe always gives the same old excuses.This carpet's getting pretty old now.
Opposite
new
5 [only before noun] former; belonging to past times or a past time in your lifeThings were different in the old days.I went back to visit my old school.Old and Middle English6 [only before noun] used to refer to something that has been replaced by something elseWe had more room in our old house.
Opposite
new
7 [only before noun] known for a long timeShe's an old friend of mine (= I have known her for a long time).We're old rivals. compare recent
 

good old/poor old

8 [only before noun] (informal) used to show affection or a lack of respectGood old Dad!You poor old thing!I hate her, the silly old cow!
Idioms

any old how

(informal) in a careless or untidy wayThe books were piled up all over the floor any old how.

any old…

(informal) any item of the type mentioned (used when it is not important which particular item is chosen)Any old room would have done.

as old as the hills

very old; ancient

for old times' sake

if you do something for old times' sake, you do it because it is connected with something good that happened to you in the past

the good/bad old days

an earlier period of time in your life or in history that is seen as better/worse than the present
That was in the bad old days of rampant inflation.

of old

(formal or literary) in or since past timesin days of oldWe know him of old (= we have known him for a long time).

old boy, chap, man, etc.

(old-fashioned, British English, informal) used by older men of the middle and upper classes as a friendly way of addressing another man

old enough to be somebody's father/mother

(disapproving) very much older than somebody (especially used to suggest that a romantic or sexual relationship between the two people is not appropriate)

old enough to know better

old enough to behave in a more sensible way than you actually did

(have) an old head on young shoulders

used to describe a young person who acts in a more sensible way than you would expect for a person of their age

the (same) old story

what usually happens
It's the same old story of a badly managed project with inadequate funding.

an old wives' tale

(disapproving) an old idea or belief that has been proved not to be scientific

one of the old school

an old-fashioned person who likes to do things as they were done in the past
see also old school
more at a chip off the old block at chip n., (there's) no fool like an old fool at fool n., a/the grand old age at grand adjective, a/the grand old man (of something) at grand adjective, give somebody the (old) heave-ho at heave-ho, have a high old time at high adjective, money for jam/old rope at money, a/the ripe old age (of…) at ripe, settle an old score at settle v., (you can't) teach an old dog new tricks at teach, (as) tough as old boots at tough adjective, be up to your (old) tricks at trick n.
Usage noteUsage note: oldelderly aged long-lived matureThese words all describe somebody/something that has lived for a long time or that usually lives for a long time.old having lived for a long time; no longer young:She's getting old—she's 75 next year.elderly (rather formal) used as a polite word for ‘old’:She is very busy caring for two elderly relatives.aged (formal) very old:Having aged relatives to stay in your house can be quite stressful.long-lived having a long life; lasting for a long time:Everyone in my family is exceptionally long-lived.mature used as a polite or humorous way of saying that somebody is no longer young:clothes for the mature womana(n) old/elderly/aged/long-lived/mature man/womana(n) old/elderly/aged/mature gentleman/lady/coupleUsage noteUsage note: older / elderThe usual comparative and superlative forms of old are older and oldest:My brother is older than me. The palace is the oldest building in the city. In British English you can also use elder and eldest when comparing the ages of people, especially members of the same family, although these words are not common in speech now. As adjectives they are only used before a noun and you cannot say ‘elder than’:my older/elder sister the elder/older of their two children I’m the eldest/oldest in the family.