Line in letter read out? (5)
I believe the answer is:
queue
'line' is the definition.
(queue is a kind of line)
'letter read out?' is the wordplay.
'letter' becomes 'cue' (I've seen this in another clue).
'read out?' indicates a 'sounds like' (homophone) clue (I've seen 'read out' mean this).
'cue' is a homophone of 'QUEUE'.
'in' is the link.
(Other definitions for queue that I've seen before include "Buyers' line" , "Stand in line" , "Very British assembly" , "Form a line" , "orderly people?" .)