US inventor increasingly impeded by sun (5)
I believe the answer is:
morse
'us inventor' is the definition.
(Samuel Morse, inventor of Morse code)
'increasingly impeded by sun' is the wordplay.
'increasingly' becomes 'more'.
'impeded by' means one lot of letters goes inside another.
'sun' becomes 's'.
'more' placed around 's' is 'MORSE'.
(Other definitions for morse that I've seen before include "& 24 Across Encrypted language" , "Walrus - TV detective" , "Dot-dash code inventor" , "10 [SLEUTH]" , "TV Oxford cop" .)