Make a remark that's dreadfully verbose (7)
I believe the answer is:
observe
'make a remark' is the definition.
(synonyms)
'dreadfully verbose' is the wordplay.
'dreadfully' indicates an anagram (a dreadful spelling).
'verbose' with letters rearranged gives 'OBSERVE'.
'that's' is the link.
(Other definitions for observe that I've seen before include "Pay attention" , "Keep; notice" , "Watch attentively" , "See - keep - remark - maintain - celebrate" , "Spot, watch" .)