Remote lake shown in poster (7)
I believe the answer is:
slender
'remote' is the definition.
(thesaurus)
'lake shown in poster' is the wordplay.
'lake' becomes 'l'.
'shown in' indicates putting letters inside.
'poster' becomes 'sender' (I've seen this before).
'l' going within 'sender' is 'SLENDER'.
(Other definitions for slender that I've seen before include "Barely sufficient; thin" , "inadequate" , "with a narrow outlook" , "Shakespearean character" , "Ann Page's suitor" .)