Abarim Publications' online Biblical Greek Dictionary
The adjective αγαθος (agathos) means good, virtuous or beneficial. It describes a tricky concept, especially since all things work for good for those who love God (Romans 8:28), but it's probably okay to assume that any movement or effort toward the inevitable and ultimate attractor of the whole of cosmic evolution (see Revelation 21:2) can be considered good, whereas any movement or effort away from that is a waste of time and energy and thus not good.
But since the inevitable and ultimate attractor of the whole of cosmic evolution is deeply akin its most fundamental principle, namely freedom (see Galatians 5:1), any restriction of movement isn't good, and goodness has rather to do with liberty than with direction. The full definition of goodness cannot easily be shoehorned into the mere handful of dimensions our language supplies, but there seems to be an arrow to liberty, just like there is one to time and in fact even complexity itself.
Our adjective is used 102 times, see full concordance, and from it derive:
- The verb αγαθοποιεω (agathopoieo), meaning to do good, which is as tricky an activity as its adjective pertains. But since ultimately all souls will fully connect, the activity described by the noun αγαπη (agape) is probably a great place to start. Our verb is used a mere 11 times, see full concordance, and from it in turn derive:
- The noun αγαθωσυνη (agathosune), meaning goodness, that is a quality pertaining to the positive direction of liberty. It's used 4 times; see full concordance.
- Together with the adjective φιλος (philos), meaning beloved: The adjective φιλαγαθος (philagathos), meaning loving what is good or virtue-loving (Titus 1:8 only). From this word derives: