convalesce: [15] Latin valēre meant ‘be strong or healthy’ (from it English gets valiant, valid, valour, and value). Derived from it was valēscere ‘grow strong’, which, with the addition of the intensive prefix com- produced convalēscere, source of English convalesce. It was quite a commonly used word in Scottish English from earliest times, but does not seem to have established itself south of the border until the 19th century. => valiant, valid, valour, value
convalesce (v.)
late 15c., from Latin convalescere "thrive, regain health," from com-, intensive prefix (see com-), + valescere "to begin to grow strong," inchoative of valere "to be strong" (see valiant). Only in Caxton and Scottish writers until 19c. Related: Convalesced; convalescing.