Missing link's first love gutted scientist (4)
I believe the answer is:
lost
'missing' is the definition.
(similar in meaning)
'link's first love gutted scientist' is the wordplay.
'link's first' becomes 'l' (1st letter of 'link').
'love' becomes 'o' (love means zero in tennis).
'gutted' says to hollow out the word (remove centre letters) (to gut something is to remove its insides).
'scientist' with its centre removed is 'st'.
'l'+'o'+'st'='LOST'
(Other definitions for lost that I've seen before include "Mislaid or was defeated" , "TV show" , "confused" , "Mislaid or strayed" , "Not knowing one's whereabouts" .)