conjunction. Except on the condition that; except under the circumstances that.

preposition. Except for; except.

If it be not that; if it be not the case that; were it not the fact that; if … not; supposing that … not.

For fear that; in case; lest.

[By omission of a verb, implied in the context, unless may have the force of ‘except,’ ‘but for’: as

Synonyms Except, Unless. Except could once be used as a synonym for unless, but the words have now drawn entirely apart. Unless is only a conjunction; except is only a preposition. Except introduces an exception to a statement which is otherwise general: it may be followed by a clause when connection is made by a particle, as when, that, as, while, or especially another preposition: the omission of such connective makes the structure archaic. Unless introduces a clause, or the abbreviation of a clause, indicating a limitation or condition.

conjunction. Upon any less condition than (the fact or thing stated in the sentence or clause which follows); if not; supposing that not; if it be not; were it not that; except.

conjunction. Except on a specified condition; if not.

"You continue thus to deal out the entire pack in successive rows, each row completely blocking the preceding one unless the removal of a card releases the one above it, or _unless the removal of cards in the upper rows_ (Rule II) releases that card from above."

if  

precisely unless  unless and until  unlesss  until and unless  

Bess  Es  Etess  Fs  Hess  

aside from  bar  barring  beside  besides