Hello everyone, nice to welcome you on our site, this page even has Level 4 answers. I enjoy it =D
Level 4 - URMONIF
The answer to this puzzle is:
Words: ONIUM, MORN, FINO, NOIR, MUNI, IRON, MUON, FOIN, FIRN, NORI, INRO, MOR, FRO, URN, RIM, FUN, RUN, RUM, OUR, FOR, NOR, FUR, FIN, FIR, NOM, MON, ION, ROM
Bonus words:
ONIUM, MORN, FINO, NOIR, MUNI, IRON, MUON, FOIN, FIRN, NORI, INRO, MOR, FRO, URN, RIM, FUN, RUN, RUM, OUR, FOR, NOR, FUR, FIN, FIR, NOM, MON, ION, ROM