Okay, to understand Epicurus's limits, we have to know what words he used. You knew this was coming, right?
Below are selections where English uses the word limit. I wanted to see if Epicurus consistently used the same or different words in the original. This is NOT an exhaustive list. If you're curious about a text not listed, just ask. The primary words Epicurus seems to use are horizō and peras and their variations. See below.
Fr. 548. Happiness and bliss are produced not by great riches nor vast possessions nor exalted occupations nor positions of power, but rather by peace of mind, freedom from pain, and a disposition of the soul that sets its limits in accordance with nature.
Fr. 548. τὸ εὔδαιμον καὶ μακάριον [happiness and blessedness] οὐ χρημάτων πλῆθος οὐδὲ πραγμάτων ὄγκος οὐδʼ ἀρχαί τινες ἔχουσιν οὐδὲ δυνάμεις, ἀλλʼ ἀλυπία (alupia "no pain") καὶ πραότης παθῶν (praotēs pathōn "mildness/gentleness of the pathē) καὶ διάθεσις ψυχῆς [psychēs "soul, mind"] τὸ κατὰ φύσιν ὁρίζουσα.
ὁρίζουσα (horizousa) < fem. participle of ορίζω (horizō) = to divide or separate from, as a boundary. (Note: This is the origin of English "horizon")
So to pare down that fragment: Happiness and bliss... are produced by peace of mind, freedom from pain, and a mind's disposition that sets its limits in accordance with nature.
PD 3. The limit of the magnitude of pleasure (is) the whole of the removal of that which causes pain. Where that which gives pleasure exists, during the time it is present, there is neither pain nor that which causes pain in body or mind nor either of these together.
PD 3. Ὅρος τοῦ μεγέθους τῶν ἡδονῶν ἡ παντὸς τοῦ ἀλγοῦντος ὑπεξαίρεσις. ὅπου δ’ ἂν τὸ ἡδόμενον ἐνῇ, καθ’ ὃν ἂν χρόνον ᾖ, οὐκ ἔστι τὸ ἀλγοῦν ἢ τὸ λυπούμενον ἢ τὸ συναμφότερον.
Ὅρος (horos) limit, rule, standard. A boundary or marker stone (compare horizō)
Horos and horizō are also used in PD 11 to state the limits of pains and desires, PD 15 to describe that "Nature's treasures have boundaries"
VS 25 uses horizō. Poverty is great wealth if measured by *the goals of nature* (tō tēs physeōs telei (< telos)) , and wealth is abject poverty if not limited (horizoumenos) by the goals of nature. ἡ πενία μετρουμένη τῷ τῆς φύσεως τέλει μέγας ἐστὶ πλοῦτος· πλοῦτος δὲ μὴ ὁριζόμενος μεγάλη ἐστὶ πενία.
PD 10. If the objects which are productive of pleasures to profligate persons really freed them from fears of the mind—the fears, I mean, inspired by celestial and atmospheric phenomena, the fear of death, the fear of pain—if, further, they taught them to limit their desires, [then] we should not have any reason to censure such persons, for they would then be filled with pleasure to overflowing on all sides and would be exempt from all pain, whether of body or mind, that is, from all evil.
PD 10. Εἰ τὰ ποιητικὰ [τῶν περὶ τοὺς ἀσώτους ἡδονῶν] ἔλυε τοὺς φόβους τῆς διανοίας τούς [τε περὶ μετεώρων καὶ θανάτου καὶ ἀλγηδόνων], ἔτι τε "τὸ πέρας τῶν ἐπιθυμιῶν" (to peras tōn epithumiōn "the end/extremity of desires") ἐδίδασκεν (taught), οὐκ ἄν ποτε εἴχομεν ὅ τι μεμψαίμεθα αὐτοῖς, πανταχόθεν ἐκπληρουμένοις τῶν ἡδονῶν καὶ οὐδαμόθεν οὔτε τὸ ἀλγοῦν οὔτε τὸ λυπούμενον ἔχουσιν, ὅ περ ἐστὶ τὸ κακόν.
πέρας peras "end, limit, boundary, goal, that which comes to an end" Peras is sometimes opposed to archē "the beginning, origin" Note that pleasure is termed in one place by Epicurus as the archē and telos (goal, fulfillment) of the blessed life.
So now we have horizō and peras.
Peras is the word used in PD 18 in "The limit of pleasure in the mind is obtained by calculating the pleasures themselves and the contrary pains, which cause the mind the greatest alarms."
PD 19 is interesting! Check it out!
Infinite and finite time afford equal pleasure, if one measures its limits by reason.
19 Ὁ ἄπειρος χρόνος ἴσην ἔχει τὴν ἡδονὴν καὶ ὁ πεπερασμένος, ἐάν τις αὐτῆς τὰ πέρατα καταμετρήσῃ τῷ λογισμῷ.
Peras (in plural πέρατα perata) is the word used for "measure its limits". But check out the word for infinite ἄπειρος apeiros < a + peras!! "No end"! The word literally means "it never ends".
Perata again used in PD 20: The flesh assumes the *limits* of pleasure to be infinite, and only infinite time would satisfy it. But the mind, grasping in thought what the end (telos) and *limit* of the flesh is, and banishing the terrors of futurity, procures a complete and perfect life and has no longer any need of infinite time.
Again in PD 21: the limits of life (ta perata tou biou)
These are some of the peras synonyms given by Woodhouse, S. C. (1910) English-Greek Dictionary A Vocabulary of the Attic Language:
accomplishment, bound, cessation, completion, conclusion, culmination, finality, finish, fulfilment, goal, measure, period.
It seems to imply something that has a natural boundary or that has come to some natural end or has been determined to have a boundary (had a boundary marker set).
Consider too the Greek preposition Peri "around" (e.g., perimeter).