Posterior?
Dorsal is the back , along the spine, i.e., a dorsal fin on a fish, a person laying on their back is said to be in a dorsal recumbant position.
"Program," "App," and "Application" are synonymous with "Software"
Opposite, reverse...
luminosity is synonymous to brightness
Dorsal comes from the Latin word dorsum, meaning the back.
The dolphin has a dorsal fin.
"High-quality and luxury are often synonymous in the minds of consumers looking for premium products."
Decrease
Syonymous is the adjectival form of synonym.
You've spelled the word "synonymous" correctly :)
extend
Necessary, important