Measurement

[Mike Curtis]

what is a unit of chain length in britain equal to 75 feet

[dave head]

it's a shot

[mikewith]

As a follow-up, bigmack had the most complete answer: "answer is shot (equivalent to 12 and half fathoms) see www.dictionary.com (I usially enter via www.onelook.com - great site for getting words when you only have a few letters by use of wildcards". So, the answer to this crossword question is: shot.