Bend sinister at the bottom in shield (7)
I believe the answer is:
buckler
'bottom in shield' is the definition.
'buckler' can be an answer for 'shield' (synonyms). I am unsure of the 'bottom in' bit.
'bend sinister at' is the wordplay.
'bend' becomes 'buckle' (I've seen this before).
'sinister at' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'buckle'+'r'='BUCKLER'
'the' is the link.
Can you help me to learn more?
(Other definitions for buckler that I've seen before include "likely to give way under pressure?" , "Small round shield" , "gives way under pressure?" , "Small shield for the forearm" .)