1. Functioning in a supporting capacity
   - auxiliary, subsidiary, supplementary 
2. Added to complete or make up a deficiency
   - supplementary

See also: additive, secondary, supplement

Encyclopedia: Supplemental

• dark-gray
• dark-green
• dark-grey
• dark-haired
• dark-skinned
• dark-spotted
• darken
• darkened
• darkener
• darkening
• darkey
• darkie
• darkish
• darkle
• darkling
• darkling beetle
• darkling groung beetle
• darkly
• darkness
• darkroom
• darksome
• darky
• darling
• darling pea
• Darling River