1. Burdened by cares
   "all ye that labour and are heavy-laden"
   - care-laden 
2. Bearing a physically heavy weight or load
   "a heavy-laden cart"
   - burdened, loaded down

See also: encumbered, troubled

• family Oestridae
• family Ogcocephalidae
• family Oleaceae
• family Oleandraceae
• family Onagraceae
• family Oniscidae
• family Ophidiidae
• family Ophiodontidae
• family Ophioglossaceae
• family Opisthocomidae
• family Opisthognathidae
• family Orchestiidae
• family Orchidaceae
• family Orectolobidae
• family Oriolidae
• family Ornithorhynchidae
• family Orobanchaceae
• family Orycteropodidae
• family Oscillatoriaceae
• family Osmeridae
• family Osmundaceae
• family Osteoglossidae
• family Ostraciidae
• family Ostraciontidae
• family Ostreidae