Sentimental type initially involved with Marconi (8)
I believe the answer is:
romantic
'sentimental' is the definition.
(I've seen this before)
'type initially involved with marconi' is the wordplay.
'initially' suggests taking the first letters.
'involved with' indicates an anagram (involved can mean confusing or complex).
The first letter of 'type' is 't'.
't' mixed up with 'marconi' makes 'ROMANTIC'.
(Other definitions for romantic that I've seen before include "Soulful or amorous idealist" , "Coin mart (anag.)" , "Amorous, showing loving feeling" , "Amorous (but not practical?)" , "Fantastic" .)