litotes

1. Deliberate understatement, especially when expressing a thought by denying its opposite. (Silva Rhetoricae)

2. A form of understatement, and implication of more than the words say. (Garrett Epp)

3. Litotes, smallnesse, or extenuation: a figure when lesse is said then signified: hereby sometimes a word is put d[...]wn with a sign of negation, when as much is signified as if we had spoken affirmatively; if not more, &c.; Litotes, tenuitas, tenuity, smalness or finenesse, derived from [litos] tenuis, small or fine. It is a kinde of Synecdoche. A Trope when a word is put down with a sign of negation, (Note in marg: Negatio contrarii auget vim affirmationis.) and yet as much is signified as if we spake affirmatively, if not more: and by others it is called a Figure. When lesse is said then signifyed, and whereby the oratour or speaker for modesties sake seems to extenuate that which he expresses. (JG Smith)

4. Figures of thought: There are other figures to adorn the meaning of the words. All of these I include in the following brief statement: when meaning is adorned, this is the standard procedure. ... ((3) diminutio) At times, diminutio implies more in the subject than is expressed in words, and makes its point by understatement, though with moderation. (Vinsauf)

5. Litotes doth more sense than words include, And often by two negatives hath stood. (Holmes)

6. Litotes, Meiosis, or Lessening, is the figure that naturally finds a place soon after its boisterous or copious opposite, hyperbole. Hereby, while we seem to lessen, we increase the force of the expression - a striking proof of the flexibility of language when wielded with skill. Hyperbole means less than it says; litotes means more. (Macbeth)

7 a) 135. LITOTES.
In litotes a statement is made by means of the negation of its opposite; as-
"The man is no fool," for "the man is wise."
"To thee I call, but with no friendly voice"- i.e., unfriendly. (De Mille)

7 b) 166. DIMINUTION.
Diminution is the opposite of amplification, and may be defined as the lowering of the importance of any topic by the assemblage of particulars designedly introduced for the purpose of lessening its force and proper value. (De Mille)

7 c) 167. DEPRECIATION.
Depreciation is diminution associated with the feeling of contempt. (De Mille)

8. Litotes is a form of expression precisely the reverse of hyperbole. It consists in giving emphasis to an idea by using terms that convey less than the truth; as "Show thyself a man," meaning that the person spoken to is urged to put forth the noblest qualities of manhood. A common form of this figure is the denial of the contrary idea instead of a direct statement; as, "I do not think him a great man," meaning that he is not only not great, but is even inferior to most men. (Waddy)

9. LITOTES. Litotes. This Trope we make use of, when we say not so much as we think; yet such a way of speaking is often much more forcible, and makes stronger impressions upon us. It is, in short, a sort of Figure extremely decent, and never used without modesty and discretion. (Norwood, 133-134)

1. It isn't very serious. I have this tiny little tumor on the brain. —J.D. Salinger, The Catcher in the Rye (Silva Rhetoricae)

1. Running a marathon in under two hours is no small accomplishment. (Silva Rhetoricae)

2. And he nas nat right fat, I undertake .... (GProl 288 qtd. in Garrett Epp)

3. It is no small account that he makes of his own wit, or he setteth not a little by himselfe.
Here by the negations of small and little, or much, are both signified and properly amplified.

Also by denying the Superlative it takes the Positive degree thus:

He is not the wisest man in the world, or he is none of the wisest, (i e.) he is not wise at all.

This and such like formes of speaking are used for modesties sake; for it were not so seemly to say, that he lacks wit, or that he is a fool.

So, if a man had some good occasion or just cause to commend himself, he cannot by any means do it in more modest manner then by this form of speech, as if he should say:

I was not the last in the field to engage the enemies of my Countrey.

Here, if he should have said, I was first, or one of the foremost in the field, although he had spoken never so truly, it would have savoured of arrogancy and boasting. (JG Smith)

4. ((3) Diminutio) Powerful Father, you whose power is by no means brief, be mindful of vengeance. (Vinsauf)

5. I neither praise your Gifts, nor despise them; i.e. I dispraise your Gifts, yet I accept them. (Holmes)

6. When we say "the man is no fool," we are understood to admit that he is wise. (Macbeth)

6. Chaucer, of his fat, rosy monk, affirms-
"He was not pale as a forpined ghost." (Macbeth)

7 c) Contemptuous depreciation is nowhere more forcibly expressed than in the words of Sir Robert Walpole"
"A patriot, sir? Why, patriots spring up like mushrooms. I could raise figure of them in four-and-twenty hours." (De Mille)

9. What, shall I praise you in this? I praise you not. Rom. 11. 21. Which was a softer way of reprehension, to tell his Romans, when they were guilty of very great irreverence in the blessed Sacrament, that he could not much commend them, upon that account; and though the expression seems very mild, and favourable, and genteel, what shall I say unto you? I praise you not. Yet it really signifies thus much, I do highly blame, and discommend such kind of practices. (Norwood, 134)