direct and unreserved in speech; straightforward; sincere

Her criticism of my work was frank but absolutely fair.

without inhibition or subterfuge; direct; undisguised

a frank appeal for financial aid.

Pathology . unmistakable; clinically evident

frank blood.

Archaic . liberal or generous.

Obsolete . free.

a signature or mark affixed by special privilege to a letter, package, or the like to ensure its transmission free of charge, as by mail.

the privilege of franking letters, packages, etc.

a franked letter, package, etc.

to mark (a letter, package, etc.) for transmission free of the usual charge, by virtue of official or special privilege; send free of charge, as mail.

to convey (a person) free of charge.

to enable to pass or go freely

to frank a visitor through customs.

to facilitate the comings and goings of (a person), esp. in society

A sizable inheritance will frank you faster than anything else.

to secure exemption for.

Carpentry . to assemble (millwork, as sash bars) with a miter joint through the moldings and a butt joint or mortise-and-tenon joint for the rest.

adjective

devious , dishonest , evasive , insincere , secretive

adjective

aboveboard , apparent , artless , bare-faced , blunt , bold , brazen , call a spade a spade , candid , direct , downright , easy , familiar , flat-out * , forthright , free , from the hip , guileless , heart-to-heart , ingenuous , lay it on the line , like it is , matter-of-fact , naive , natural , open , outright , outspoken , plain , plain-spoken , real , saying what one thinks , scrupulous , sincere , straight , straightforward , transparent , truthful , unconcealed , undisguised , uninhibited , unreserved , unrestricted , up front , upright , honest , man-to-man , plainspoken , straight-out , bluff , brusque , carefree , communicative , curt , demonstrative , explicit , forthcoming , foursquare , gruff , informative , manifest , no-nonsense , profuse , simple , unconstrained , unvarnished , up-front