concerning crossword clue

 The crossword clue "concerning" can have multiple answers, depending on the length of the answer word that is being sought.

Here are some possible answers for a 4-letter word:

RE

AS TO

ASTO

Here are some possible answers for a 5-letter word:

ABOUT

APROPOS

ANENT

Here are some possible answers for a 6-letter word:

IN RE

REGARDING

RELATIVE TO

I hope this helps! Let me know if you have any other questions.