Giggle, gaggle, legging
A roo. Not sure if that's officially in the English dictionary, but that's how a lot of Aussies refer to them.
Set has the most definitions in an unabridged dictionary.
The three letter word for donkey is ass. Check it in the dictionary.
triennium (concise oxford English dictionary)
The word "tattletale" contains the letter T three times.
macerate
The first written number in the English language that contains the letter "a" is "one thousand." In terms of numerical representation, this is the first instance where the letter appears. Prior to that, numbers like "one," "two," or "three" do not include the letter "a."
"Blue" in English is the three-letter word blu in Italian.
There are very many three-letter acronyms in the dictionary, including government agencies (like FDA), titles (like DDS), etc.
deeded - to be given the deeds to somewhere/something
There are no six-letter words containing three L's in either the Scrabble dictionary, or Webster's Second International dictionary, (250,000+ words).
Words in the dictionary are arranged alphabetically. Because all three of these words share the first three letters "uni-", we must look at the fourth letter. The fourth letter of "unicorn" is "c", and the fourth letter of "union" is "o". Since "c" comes before "f" and "o" comes after, the word "union" will come after "uniform" in the dictionary.