School nowadays is gloomy (3)
I believe the answer is:
sad
'gloomy' is the definition.
(similar in meaning)
'school nowadays' is the wordplay.
'school' becomes 'S'.
'nowadays' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
's'+'ad'='SAD'
'is' acts as a link.
(Other definitions for sad that I've seen before include "Melancholy, triste" , "Sorrowful, unhappy" , "Morose" , "Mournful - sorry" , "Melancholy or pitiful" .)