Lofty is beginning to tower over everyone (4)
I believe the answer is:
tall
'lofty' is the definition.
(synonyms)
'beginning to tower over everyone' is the wordplay.
'beginning to' indicates taking the first letters.
'over' says to put letters next to each other (in a down clue, some letters go over others).
'everyone' becomes 'all' (all people).
The initial letter of 'tower' is 't'.
't'+'all'='TALL'
'is' acts as a link.
(Other definitions for tall that I've seen before include "hard to believe in" , "Unbelievable" , "that's hard to swallow" , "Lofty; unlikely" , "Higher than the average person" .)