What's a word that means to 'intentionally withhold information'?

single-word-requests

I was reading an online editorial a week or so ago in which its author employed an awesome word, the meaning of which was "to intentionally and deliberately withhold information [essential to the endeavor at hand, with the underlying purpose of misleading others by its omission]". Yeah, all of that in one word.

Alas, I can't seem to find the editorial online anymore, I've now I forgotten the word!

I think you're looking for dissimulate (or dissemble); alternatives include prevaricate (avoid a direct answer) equivocate (give an ambiguous answer: "you will emerge from the war with the Romans victorious"), and obfuscate (give a confusing answer that serves to hide the real information), but all of those require you to say something. Only dissimulate implies you say nothing at all: a lie of omission (cf. lie of commission).

On a different tack, there is both non-disclosure and maintaining confidentiality, which both mean to purposefully withhold information, but usually the intent is to protect one's own interests, rather than mislead.

To keep mum (and synonyms) is similar, except that's typically applied to someone who has transgressed (or knows about someone who has) in some way.

One answer could be "Tergiversate".

From dictionary.reference.com-

tergiversate — vb

to change sides or loyalties; apostatize

to be evasive or ambiguous; equivocate

From Oxford Dictionaries-

tergiversate VERB

Make conflicting or evasive statements; equivocate:

An example-

the more she tergiversated, the greater grew the ardency of the reporters for an interview

Another alternative could be- pussyfoot

Merriam-Webster defines pussyfoot as

to avoid making a definite decision or stating a definite opinion because of fear, doubt, etc.

Some more synonyms you could use are fudge, hedge, equivocate, but I'm not sure how well they describe the situation you have in mind.

Possibly stonewall

stalling, evading, or filibustering, especially to avoid revealing politically embarrassing information.

http://dictionary.reference.com/browse/Stonewall

Similar to filibuster

A word that means “withhold information (possibly) for the purpose of misleading others by its omission” is censor:

Merriam-Webster:

to suppress or delete as objectionable <censor out indecent passages>

Cambridge English Dictionary:

to remove parts of something, such as a book, movie, or letter, that you do not want someone to see or hear:
She opposes efforts to censor the Internet.

English Oxford Dictionaries:

Examine [an object] (a book, film, etc.) officially and suppress unacceptable parts of it:
‘the report had been censored “in the national interest” ’
‘the letters she received were censored’

Collins Dictionary:

to ban or cut portions of (a publication, film, letter, etc)

A simple form of censorship is total suppression of information, but that would likely be obvious, and therefore not misleading. A more effective technique is selective suppression; e.g., blocking the publication or broadcast of certain stories while allowing others. (If you aren’t informed that a certain organization is rife with fraud, waste, and abuse, you might be misled into thinking that they are ethical and efficient.) One specific form of censoring documents (especially printed [hardcopy] documents) is redacting or redaction.

redact:

Merriam-Webster:

to select or adapt (as by obscuring or removing sensitive information) for publication or release

to obscure or remove (text) from a document prior to publication or release

Cambridge English Dictionary:

to remove words or information from a text before it is printed or made available to the public:
Officers’ names are routinely redacted from any publicly released reports.
Some parts of secret files are available to the public, but heavily redacted.

English Oxford Dictionaries:

Edit (text) for publication:
‘a confidential memo which has been redacted from 25 pages to just one paragraph’

Censor or obscure (part of a text) for legal or security purposes.

See this discussion of redact on EL&U: Is “redact” an acceptable substitute for “delete” or “omit?”

Here are some examples of redacted documents; one lightly redacted, one heavily:

lightly redacted document heavily redacted document
^{Original image URLs: https://jeffpelline.files.wordpress.com/2011/04/redacted1.png and https://upload.wikimedia.org/wikipedia/commons/5/53/Aclu-v-ashcroft-redacted.jpg}