exteri, exterior, _outer_ extrēmus, extimus,
_foreigners_, _outermost_.
nātiōnēs exterae,
_foreign nations_,
inferī, _gods of the īnferior, _lower_, īnfimus, īmus,
lower world_, _lowest_.
Mare Inferum,
_Mediterranean Sea_,
superī, _gods superior, _higher_, suprēmus, _last_.
above_, summus, _highest_.
Mare Superum,
_Adriatic Sea_,

3. Comparative lacking.

vetus, _old_, ----[17] veterrimus.
fīdus, _faithful_, ---- fīdissimus.
novus, _new_, ----[18] novissimus,[19] _last_.
sacer, _sacred_, ---- sacerrimus.
falsus, _false_, ---- falsissimus.

Also in some other words less frequently used.

4. Superlative lacking.

alacer, _lively_, alacrior, ----
ingēns, _great_, ingentior, ----
salūtāris, _wholesome_, salūtārior, ----
juvenis, _young_, jūnior, ----[20]
senex, _old_, senior. ----[21]