Abarim Publications' online Biblical Greek Dictionary
The noun γαλα (gala) means milk, and survives in the English term "galactic acid". Our noun's genitive form is galaktos, hence the name galaktos kuklos or Milky Circle for our English word "galaxy" or Milky Way.
Paul uses our noun to indicate with what a shepherd (ποιμην, poimen) is additionally rewarded as perk of the job (1 Corinthians 9:7) but mostly this word is used as metaphor for baby food, or "elementary principles" (Hebrews 5:12-14), as opposite to the solid food of more advanced insights obtained by practice (1 Corinthians 3:2, 1 Peter 2:2). Our word occurs a total of 5 times in the New Testament; see full concordance.
In both the Roman and the Greek worlds, milk was proverbially recognized not only as white but also as sweet and pleasant. The Greek goddess of love, Aphrodite, was reportedly born at Paphos, Cyprus, and depicted in a dashing ivory statue, which she subsequently brought to life. This statue became known as Galatea (Milky) not simply because it was white (all ivory statues are white) but also because it represented the deity of love.
The connection between milk and sweetness is possibly due to milk's taste, but probably more so because it's mostly associated to infanthood and juvenile joy and lack of worries. It is probably also relevant that the haplotype needed to digest milk as an adult first developed in northern Europe (relatively simply studies of the spread of lactose intolerance show this). That means that adult milk drinkers are able to retain some of the bliss of being a child (Matthew 18:3).
In the Bible, the importance of training and practice is often emphasized, but unlike disciplines like science and yoga, which promise bliss at the end of long training programs, the joy of knowing the Lord of Life starts at the beginning of it. All training in the Biblical sense is done within that initial joy, and more joy can always be drawn from the most elementary principles of salvation.
Note that the Latin word gallus means rooster and probably derives from a Sanskrit verb that gave us the English verbs "to call" and "to cry" (and the Greek verb καλεω, kaleo, meaning to call). And that means that to the ancients, milk was probably known primarily as a substance specifically related to crying things (such as babies).