Be adequate (7)
'be adequate' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for suffice that I've seen before include "Be enough" , "Be adequate" , "Serve - do" .)
(Other definitions for serve that I've seen before include "commence action in court before judges?" , "Deliver" , "Perform duties for" , "Begin a tennis game" , "Be adequate; put ball in play" .)