One on the pull could get an erection (5)
I believe the answer is:
tower
'an erection' is the definition.
(thesaurus)
'one on the pull could' is the wordplay.
'one on' says to put letters next to each other.
'the pull' becomes 'tow' (tow is a kind of pull).
'could' becomes 'er' (I can't explain this - if you can you should believe this answer much more).
'tow'+'er' is 'TOWER'.
'get' is the link.
Can you help me to learn more?
(Other definitions for tower that I've seen before include "Stand very high (over)" , "Monument" , "famous prison" , "See 4 Down" , "Perhaps keep" .)