Studies grass say at start of semester (5)
I believe the answer is:
reads
'studies' is the definition.
('read' can be a synonym of 'study')
'grass say at start of semester' is the wordplay.
'grass' becomes 'reed' (I've seen this before).
'say' shows a homophone (sound like).
'at start of' says to take the initial letters (I've seen 'at start' mean this).
The first letter of 'semester' is 's'.
'reed' sounds like 'read'.
'read'+'s'='READS'
(Other definitions for reads that I've seen before include "Studies (at university)" , "Looks at and undertsands the written word" , "Scans" , "Understands written language" , "Peruses" .)