double
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Answer #2:
IMHO, I don't think 'double' does the job, any better than 'triple' or 'quintuple' might.
If you really need an 'opposite' for 'single', my suggestion is that 'multiple' is about
the best you're going to get. (That's of course steering clear of 'married'.)
The opposite of single is "taken" or "in a relationship".
taken
What is 9plus10
multiple
A single person.
Single faith.
The opposite of a mass battle could be single combat : a duel or bout. There is no direct opposite meaning "not" a pitched battle.
Regarding "single" to be unmarried, the opposite is a married person, or spouse.
Reverse single crochet means to turn the item the opposite way you were crocheting and single crochet as normal-just in the opposite direction. For instance if you crochet from right to left as normal, you would chain one, turn the item around so you are facing the opposite side (the 'wrong side') and single crochet around. The stitches will then face the opposite way from the rest giving it a decorative edge.
There isn't really an antonym for audience. There are many synonyms for it as well as phrases that mean the opposite, but not single words that mean the opposite.
There is no single-word opposite of "permeate," which means to spread throughout an area or to pass through a membrane.
The opposite status of a chemical compound could be an element, or a mixture. The opposite of the adjective compound (multiple) could be single. For sentences, the opposite of a compound sentence is a simple sentence.
An autoantonym is a single word which can have two completely opposite meanings.