ar- (2), also ari-, prefix for superlative (compare arya #1, 2), hence arcalima "brightest", arimelda *"dearest" (PE17:56-57). In the grammar described in the source, this prefix was to express superlative as the highest degree (in actual comparison), whereas the alternative prefix an- rather expressed "very" or "exceedingly" with a more purely augmentative or adverbial force, but these distinctions do not seem to have been clearly present at all stages of Tolkiens work. See an- #2, am- #2.
Quenya
melda
beloved, dear, sweet
melda
adjective. dear, beloved, beloved, dear, [ᴹQ.] sweet
a arimelda na epe b
A is (very much) [dearer] than B
a arimelda na ilyaron
A is dearest of all
ar-
brightest
a anamelda na ar ilyan
A is dearest of all
a anamelda na ep’ ilya
A is dearest of all
a ancalima imb’ illi
A is brightest of all
arcalima ar eleni
A is brightest of all
melin
dear
melin adj. "dear" (MEL)
sonda
dear, fond
[sonda adj. "dear, fond" (VT46:15)]
melda adj. "beloved, dear, sweet" (MEL, VT45:34), superlative arimelda *"dearest" (PE17:56, see ar- #2), meldielto "they are beloved" (sc. meld[a]-ië-lto "beloved-are-they" however, both the stative verb ending -ië "is/are" and the ending -lto "they" may be obsolete in LotR-style Quenya) (FS) PE17:55 gives the comparative form as arimelda or ammelda and the superlative as eremelda, anamelda or once again ammelda (PE17:55).