Pineapple class to admit unmarried men (7)
I believe the answer is:
grenade
'pineapple' is the definition.
(I've seen this before)
'class to admit unmarried men' is the wordplay.
'class' becomes 'grade' (grading is a kind of classing).
'to admit' indicates putting letters inside.
'unmarried men' becomes 'en' (I can't explain this - if you can you should believe this answer much more).
'grade' going around 'en' is 'GRENADE'.
Can you help me to learn more?
(Other definitions for grenade that I've seen before include "Missile thrown" , "Small explosive device" , "One might go off" , "hand-held missile" , "Small hand-bomb" .)