After vacation, teacher with ambition to be widely discussed (5)
I believe the answer is:
trend
'to be widely discussed' is the definition.
(as in trending online)
'after vacation teacher with ambition' is the wordplay.
'after vacation' says to hollow out the word (remove centre letters) (the inside letters must vacate).
'with' says to put letters next to each other.
'ambition' becomes 'end' ('end' can mean a goal or purpose).
'teacher' with its middle removed is 'tr'.
'tr'+'end'='TREND'
(Other definitions for trend that I've seen before include "General tendency" , "shift" , "Bias" , "Leaning; fashion" , "Style, vogue" .)