Adjective

(en adjective)

Belonging to, concerning, or accessible only to an individual person or a specific group.

* {{quote-magazine, date=2013-06-14, author=(Jonathan Freedland)

, volume=189, issue=1, page=18, magazine=(The Guardian Weekly) , title= Obama's once hip brand is now tainted , passage=Now we are liberal with our innermost secrets, spraying them into the public ether with a generosity our forebears could not have imagined. Where we once sent love letters in a sealed envelope, or stuck photographs of our children in a family album, now such private material is despatched to servers and clouds operated by people we don't know and will never meet.}}

Not in governmental office or employment.

* {{quote-magazine, date=2013-07-19, author=(Peter Wilby)

, volume=189, issue=6, page=30, magazine=(The Guardian Weekly) , title= Finland spreads word on schools , passage=Imagine a country where children do nothing but play until they start compulsory schooling at age seven. Then, without exception, they attend comprehensives until the age of 16.

Not publicly known; not open; secret.

* {{quote-book, year=1963, author=(Margery Allingham), title=(The China Governess)

, chapter=20 citation , passage=The story struck the depressingly familiar note with which true stories ring in the tried ears of experienced policemen.

Protected from view or disturbance by others; secluded.

Intended only for the use of an individual, group, or organization.

Not accessible by the public.

Not traded by the public.

* {{quote-magazine, date=2013-06-22, volume=407, issue=8841, page=70, magazine=(The Economist)

, title= Engineers of a different kind , passage=Private -equity nabobs bristle at being dubbed mere financiers. Piling debt onto companies’ balance-sheets is only a small part of what leveraged buy-outs are about, they insist. Improving the workings of the businesses they take over is just as core to their calling, if not more so. Much of their pleading is public-relations bluster.}}

Secretive; reserved.

(US, of a room in a medical facility) Not shared with another patient.

Adjective

(en adjective)

Producing harm in a stealthy, often gradual, manner.

* 1847 , George Lippard, The Quaker City: or, The monks of Monk-Hall

Strong and vigorous man as he looks, Livingstone has been for years the victim of a secret and insidious disease.

* 1997 , Matthew Wood, The book of herbal wisdom: using plants as medicine

At some point in time they may become the source of an insidious cancer.

* 2007 , Sharon Weinstein, Ada Lawrence Plumer, Principles and practice of intravenous therapy

The nurse always must be alert to signs of slow leak or insidious infiltration.

Intending to entrap; alluring but harmful.

* Nathaniel Hawthorne

The insidious whisper of the bad angel.

* 1948 , D.V. Chitaley (editor or publisher), All India Reporter , volume 3, page 341:

All these facts clearly appear to me now to establish that the sanctioned scheme was a part of a bigger and […] more insidious scheme which was to hoodwink the creditors and to firmly establish and consolidate the position […]

* 1969 , Dorothy Brewster, John Angus Burrell, Dead reckonings in fiction

The atmosphere of this insidious city comes out to meet him the moment he touches the European shore; for in London he meets Maria Gostrey just over from France.

* 2005 , Anita Desai, Voices in the City , page 189:

This seemed to her the worst defilement into which this insidious city had cheated her and in her agitation, she nearly ran into the latrine, […]

* 2007 , Joseph Epstein, Narcissus Leaves the Pool , page 171:

This is the insidious way sports entrap you: you follow a player, which commits you to his team. You begin to acquire scraps of utterly useless information about teammates, managers, owners, trainers, agents, lawyers.

Hansel and Gretel were lured by the witch’s insidious gingerbread house.

(nonstandard) Treacherous.

* 1858 , Phineas Camp Headley, The life of the Empress Josephine: first wife of Napoleon

But with whom do you contract that alliance? With the natural enemy of France — that insidious house of Austria — which detests our country from feeling, system, and necessity.

* 1912 , Ralph Straus, The prison without a wall

‘Believe me,’ he shouted, ‘these insidious folk talk dangerous nonsense. I hear they are spouting out their ridiculous platitudes not five miles from this park in which we are standing…’

The battle was lost due to the actions of insidious defectors.