Suspect let cop see instrument (9)
I believe the answer is:
'instrument' is the definition.
(telescope is a kind of instrument)
'suspect let cop see' is the wordplay.
'suspect' indicates anagramming the letters (a suspicious or unusual spelling).
'letcopsee' is an anagram of 'TELESCOPE'.
(Other definitions for telescope that I've seen before include "Instrument for viewing from afar" , "Optical instrument for distant viewing" , "Compress like optical instrument that magnifies" , "contract" , "Magnifier of distant images" .)