Derived from √REN, and partially confirmed by rîn (cf. mîl "love, affection" & mel- "to love").
Sindarin
-ren
suffix. adjective suffix
-en
suffix. adjective suffix
ren-
75$ verb. to remember
ren-
verb. to remember
-eb
suffix. adjective suffix
-iel
suffix. adjective suffix
-in
suffix. adjective suffix
@@@ perhaps a later, S-only, innovation