Lines up in the dormitory (3)
I believe the answer is:
ode
'lines' is the definition.
(I've seen this before)
'up in the dormitory' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'in' indicates the answer is hidden within the clue.
'edo' can be found hidden inside 'the dormitory'.
'edo' reversed gives 'ODE'.
(Other definitions for ode that I've seen before include "A poem celebrating person or event" , "Literary work" , "Poem in praise of doe" , "Poem expressing noble feelings" , "Poetic composition" .)