Latria is defined as that worship which is due only to God, unlike other forms of veneration (such as to the Virgin Mary or Saints) which is called Dulia and Hyperdulia. All three, I think, are forms of Adoratio.
Regarding Latria, it comes from the Greek Latreia (λατρεία), which means service and worship. In the Greek authors it could mean any service for hire (see Thayer's Greek Lexicon and LS), but came to mean the exclusive service/worship of God, being used to reference this in the Bible as mentioned by St. Augustine in De Civitas Dei (Book X, Ch. 1), where he also mentions Proskynesis - seemingly the first attempt in canon to differentiate between worship and veneration.
St. Jerome addressed this issue by saying "We do not adore, I will not say the relics of the martyrs, but either the sun or the moon or even the angels - that is to say with the worship of latria - but we honor the martyrs' relics, so that thereby we give honor to Him Whose martyrs they are." And St. Thomas Aquinas hammers out the issue most thoroughly in Summa Theologae, writing "Wherefore dulia, which pays due service to a human lord, is a distinct virtue from latria, which pays due service to the Lordship of God. It is, moreover, a species of observance, because by observance we honor all those who excel in dignity, while dulia properly speaking is the reverence of servants for their master, dulia being the Greek for servitude".
Adoration in Classical Rome "was primarily an act of homage or worship, which, among the Romans, was performed by raising the hand to the mouth, kissing it and then waving it in the direction of the adored object." First done to gods, it was later done to emperors "by bowing or kneeling, laying hold of the imperial robe, and presently withdrawing the hand and pressing it to the lips, or by putting the royal robe itself to the lips." This is detailed nicely in A Dictionary of Greek and Roman Antiquities, but LS doesn't have much to say about Adoratio, but the Catholic Encyclopedia does.
Which word should I use when saying "Worship is only for God"? Adoratio or Latria?
My problem with Adoratio is that it seems to me to contain the meanings of Dulia and Hyperdulia within it, as well as Latria, so to say 'Adoratio' is only for God would be technically incorrect (as far as Catholic Doctrine is concerned at least), since Dulia and Hyperdulia are for Saints and Mary.
And my problem with Latria is just that the statement "Latria is only for God" seems redundant since that fact is contained within the meaning of the word Latria itself. It is true, but it is more like a dictionary definition of the word then a moral/theological statement.
As for other options, it is St. Augustine himself in the above linked chapter where he complains about cultus (see LS), stating that "This cannot so well be called simply cultus, for in that case it would not seem to be due exclusively to God; for the same word is applied to the respect we pay either to the memory or the living presence of men."
Cicero defines Religio as "Cultus Deorum" ("the cultivation of the gods", De Natura Deorum 2.8 and 1.117). But Augustine is not satisfied with Religio either, writing "yet, as not only the uneducated, but also the best instructed, use the word religion to express human ties, and relationships, and affinities, it would inevitably introduce ambiguity to use this word in discussing the worship of God, unable as we are to say that religion is nothing else than the worship of God, without contradicting the common usage which applies this word to the observance of social relationships."
Update: I have found the motto Deum Solum Adorabis used on coins by Hesse (with a photograph and more details here). So in the Holy Roman Empire at least one might use Adorabis, the second-person singular future active indicative of adōrō.