Latina Vulgata: Latin Words no. 8.

Aemulatio/aemulationis (f) - zeal, jealousy.

A feminine noun of the third declension. Two slightly different meanings. It can mean 'zeal' or keenness; or it can have overtones of jealousy and envy.

Related to the English word 'emulation', which nowadays tends to mean 'trying to equal by imitation' but has an older meaning also of 'jealous rivalry'.

Scio enim promptum animum vestrum: pro quo de vobis glorior apud Macedonas. Quoniam Achaia parata est ab anno praeterito, et vestra aemulatio provocavit plurimos.
For I know your forward mind: for which I boast of you to the Macedonians. That Achaia also is ready from the year past, and your emulation [zeal] hath provoked very many.
2 Corinthians 9:2. Used here to mean zeal.

Testimonium enim perhibeo illis, quod aemulationem Dei habent, sed non secundum scientiam.
For I bear them witness, that they have a zeal of God, but not according to knowledge.
Romans 10:2. Once again, zeal.

Sicut in die honeste ambulemus: non in comesationibus et ebrietatibus, non in cubilibus et inpudicitiis, non in contentione et aemulatione.
Let us walk honestly, as in the day: not in rioting and drunkenness, not in chambering and impurities, not in contention and envy.
Romans 13:13. Here it means jealousy or envy.

Sed dico: numquid Israel non cognovit? Primus Moses dicit: ego ad aemulationem vos adducam in non gentem; in gentem insipientem in iram vos mittam.
But I say: Hath not Israel known? First, Moses saith: I will provoke you to jealousy by that which is not a nation; by a foolish nation I will anger you.
Romans 10:19. Jealousy.

Related forms

1. aemulator/aemulatoris (m) - zealous observer or imitator.

Et proficiebam in Judaismo supra multos coetaneos in genere meo, abundantius aemulator existens paternarum mearum traditionum.
And I made progress in the Jews' religion above many of my equals in my own nation, being more abundantly zealous for the traditions of my fathers.
Galatians 1:14.

2. aemulor/aemulari/aemulatum - to be zealous for, to be desirous of; or to be jealous. A deponent verb of the 1st declension.

Aemulantur vos non bene: sed excludere vos volunt, ut illos aemulemini. Bonum autem aemulamini in bono semper: et non tantum cum praesens sum apud vos.
They are zealous in your regard not well: but they would exclude you, that you might be zealous for them. But be zealous for that which is good in a good thing always: and not only when I am present with you.
Galatians 4:17-18. Three uses in the same passage. The first is present indicative; the second is present subjunctive as part of a causal clause; the third is a present imperative

Et patriarchae aemulantes Ioseph vendiderunt in Aegyptum et erat Deus cum eo.

Acts 7:9. Present participle. Meaning of 'being jealous of'.

Aemulor enim vos Dei aemulatione. Despondi enim vos uni viro virginem castam exhibere Christo.
For I am jealous of you with the jealousy of God. For I have espoused you to one husband that I may present you as a chaste virgin to Christ.
2 Corinthians 11:2. Present tense. Despite the translation, the meaning is more zeal than envy.And the patriarchs, through envy, sold Joseph into Egypt; and God was with him.