iocundus
Could not find iocundissimum in Logeion dictionaries.
iocundissimum Adjective: neuter genitive plural superlative, Adjective: neuter accusative singular superlative, Adjective: neuter vocative singular superlative, Adjective: neuter nominative singular superlative, Adjective: masculine accusative singular superlative, Adjective: masculine genitive plural superlative of iocundus
jŏcundus, a, um, v. iucundus (late Lat.), Vop. Proc. 12, 6.