Sometimes you will see a crossword clue with one of the following terms appended to it. These terms briefly indicate the type of word that the clue is describing.

"Abbr" : Abbreviation. The answer to the clue may be an acronym or contraction that has come into use as a word in its own right. (e.g. "scuba")

"Arch" : Archaic. The answer to the clue is a word that's no longer in common use, or which no longer has its former meaning. (e.g. "forsooth")

"Inf" : Informal. The answer to the clue is a slang term or nickname. (e.g. "gumshoe")