Letters giving support (7)
I believe the answer is:
trestle
'support' is the definition.
(I've seen this before)
'letters giving' is the wordplay.
'giving' is an anagram indicator (the letters give the letters for another word).
'letters' anagrammed gives 'TRESTLE'.
(Other definitions for trestle that I've seen before include "Framework to support a flat surface -- letters (anag)" , "support of growth" , "Simple table support" , "Framework for holding a tabletop" , "Supported (and supporting) board" .)