Definition of frank :
1. A French coin. See Franc.
2. A member of one of the German tribes that in the fifth century overran and conquered Gaul, and established the kingdom of France.
3. A native or inhabitant of Western Europe; a European; - a term used in the Levant.
4. A pigsty.
5. Free in uttering one's real sentiments; not reserved; using no disguise; candid; ingenuous; as, a frank nature, conversation, manner, etc.
6. Liberal; generous; profuse.
7. The common heron; - so called from its note.
8. The privilege of sending letters or other mail matter, free of postage, or without charge; also, the sign, mark, or signature denoting that a letter or other mail matter is to free of postage.
9. To extempt from charge for postage, as a letter, package, or packet, etc.
10. To send by public conveyance free of expense.
11. To shut up in a frank or sty; to pen up; hence, to cram; to fatten.
12. Unbounded by restrictions, limitations, etc.; free.
13. Unrestrained; loose; licentious; - used in a bad sense.
inconsiderate, flat-out, calling a spade a spade, rude, straight-from-the-shoulder, wienerwurst, unreserved, vocal, discourteous, forthright, open-faced, apparent, aboveboard, click, heart-to-heart, straight-shooting, blustering, impolite, bold, rough, easy, familiar, hot dog, weenie, detent, obvious, red hot, show, frump, blackguard, straight, undissembling, straight-out, guileless, firedog, free-spoken, dog, upfront, saying what one thinks, uninhibited, free, unguarded, andiron, hotdog, postmark, hound, explicit, wiener, pawl, matter-of-fact, unmannerly, brusk, frankfurter, point-blank, free in speaking, crude, abrupt, cad, uncivil, openhearted, bounder, man-to-man, coarse, domestic dog, dog-iron, bluff, plainspoken, heel
artless (part of speech: adjective)
naive, sincere, downright, undeceptive, honest, overt, broad, trusting, direct, unsophisticated, artless, outgoing, callow, candid, undisguised, unbeguiling, natural, unrestrained, plain-spoken, unaffected, open, unartful, plain, blunt, ingenuous, genuine, uncalculating, undeceitful, un-artificial, straightforward, undeceiving
truthful (part of speech: adjective)
succinct (part of speech: adjective)