adj

• (medicine) Unmistakable, clinically obvious, self-evident.
  "The research probes whether treating pre-diabetes with metformin can prevent progression to frank diabetes."
• (obsolete) Unbounded by restrictions, limitations, etc.; free.
  "It is of frank gift."
• (obsolete) Liberal; generous; profuse.
  "Frank of Civilities that cost them nothing."
• (obsolete, derogatory) Unrestrained; loose; licentious.
  "Over the fields, in his franke lustinesse, And all the champain o're he soared light."

noun

• (uncountable) Free postage, a right exercised by governments (usually with definite article).
  "October 5, 1780, William Cowper, letter to Rev. William Unwin I have said so much, that, if I had not a frank, I must burn my letter and begin again."
• (countable) The notice on an envelope where a stamp would normally be found.
  "But, although her friends were kind, Lady Anne was not easy; neither daughter made her appearance, nor did she receive a letter to account for their silence. She remembered, indeed, that Charles Penrhyn could not get franks now, and her daughters knew she would not pay postage; and she had commanded Helen to work night and day, saying, "surely they can give her common materials.""

verb

• (transitive) To place a frank on an envelope.
  "It will be so ridiculous to see all his letters directed to him with an M.P.—But do you know, he says, he will never frank for me?"
• (transitive) To exempt from charge for postage, as a letter, package, or packet, etc.
• (transitive) To send by public conveyance free of expense.
  "1850-1859, Charles Dickens, Household Words This required extensive correspondence; so, in the next place, the privilege of franking letters in reference to the emigrants' registration office, was obtained—much to the indignation of red tapists."

noun

• (UK) The grey heron.