Similar words: alongside, long, long., along, long for, prolong, all along, get along. Meaning: adv. of the distant or comparatively distant past.
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1) I have long since abandoned the notion that higher education is essential to either success or happiness. Hot houses of learning do not always grow anything edible. 
2) Dad had long since divested himself of anything valuable.
3) They had long since moved away.
4) Any doubts had long since been swept away.
5) The entrance had long since been walled up.
6) It was not long since that I returned.
7) I've long since forgiven her for what she did.
8) The city has long since passed into oblivion.
9) This idea has long since fallen out of favour.
10) How long since is it?
11) The original building has long since been demolished.
12) Her parents had long since branded her a failure.
13) I've long since forgotten what our quarrel was about.
14) It's so long since it rained that the river-bed is dry.
15) This kind of textile machines has long since been out of use.
16) I had long since grown used to the eccentricities of his driving technique.
17) The people who built this temple have long since vanished.
18) She has long since moved on from the roles of her youth.
19) The UN is an organisation which has long since outlived its usefulness.
20) Even though her parents have long since died, she still talks about them in the present tense.
21) Other staff had long since gone home.
22) He had long since given up reading the tabloids.
23) He had long since gone dead on politicians.
24) She had long since abandoned that hope.
25) I've long since stopped caring about him.
26) The soldiers have long since returned to their bases.
27) Most have long since gone, leaving behind their legacy of sunless,(http://sentencedict.com/long since.html) blanket afforestation.
28) The town outside was long since ruined and empty, and he preferred St Hilarion in the heat of the day.
29) Old tattered flags hung from the ceiling, their patterns long since faded into the air.
30) The stones of the church are dark with age and the roof has long since gone.
More similar words: alongside, long, long., along, long for, prolong, all along, get along, as long as, no longer, so long as, belong to, longtime, any longer, long-term, since, along with, before long, long before, in the long run, get along with, ever since, angst, earnings, bearings, youngster, single, singer, casino, cousin.