• unlesse (obsolete)
• unlessen
• 'less

(This etymology is missing or incomplete. Please add to it, or discuss it at the Etymology scriptorium.)

• IPA^(key): /ənˈlɛs/, /ʌnˈlɛs/

• Audio (US):

  (file)

• Rhymes: -ɛs

unless

1. Except on a specified condition; if not.

   I’m leaving unless I get a pay rise.

   You can't go out unless it stops raining.

   • 1839, Denison Olmsted, A Compendium of Astronomy, page 95:

     Secondly, When a body is once in motion it will continue to move forever, unless something stops it. When a ball is struck on the surface of the earth, the friction of the earth and the resistance of the air soon stop its motion.

   • 1971, Dr. Seuss, The Lorax:

     Unless someone like you...cares a whole awful lot...nothing is going to get better...It's not.

2. If not; used with counterfactual conditionals.
   • 1159, John of Salisbury, Policraticus, edited by Cary J. Nederman, Cambridge University Press, 1990, page 3 (Google Books view):

     Who would know of Alexander or Caesar, or would respect the Stoics or the Peripatetics, unless they had been distinguished by the memorials of writers?

   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC, 2 Samuel 2:27:

     And Joab said, As God liveth, unless thou hadst spoken, surely then in the morning the people had gone up every one from following his brother.

   • 1867, William Robinson Pirie, Natural Theology: An Inquiry Into the Fundamental Principles of Religious, Moral, and Political Science, page 75 (Google Books view):

     Unless He were omnipotent, we could not be sure of His ability to bless us.

3. Except if; used with hypothetical conditionals.
   • 1809, The Naval Chronicle for 1809: Containing a General and Biographical History of the Royal Navy of the United Kingdom with a Variety of Original Papers on Nautical Subjects. Vol. XXII. (from July to December), Cambridge University Press, 2010, page 482 (Google Books view):

     Q. If Lieutenant P. had given the word "Fire," would you have fired, and at what?—A. I should not have known, unless he had told me what to fire at.

   • 1847, Emily Brontë, chapter III, in Wuthering Heights:

     Lie down and finish out the night, since you are here; but, for heaven's sake! don't repeat that horrid noise: nothing could excuse it, unless you were having your throat cut!

   • 1981, Arthur C. Danto, The Transfiguration of the Commonplace: A Philosophy of Art, page 118 (Google Books view):

     Suppose Breugel had done the whole painting with no legs. Then, titled as it is, it would be mystifying, unless someone were to say: the boy has fallen in the waters and they have closed over him, calm is restored, life goes on (as in The Israelites Crossing the Red Sea).

• (antonym(s) of “except on a condition”): if

• precisely unless
• unlesss
• unless and until, until and unless