You can only search the suttas (here) until you find an unambiguous contextual example.
For example, AN 6.133 Arati Sutta is not unambiguous but points to 'resentment' inciting revenge:
Mendicants, there are these three things. What three? arati,
cruelty (vihiṁsā) and unprincipled conduct (adhammacariyā). These are the three things. To give
up these three things you should develop three things. What three? You
should develop rejoicing to give up arati, harmlessness to give
up cruelty and principled conduct to give up unprincipled conduct.
These are the three things you should develop to give up those three
SN 9.4 appears more clear and points to "dissatisfaction":
Seeing so many vacated seats today, Arati viya mejja khāyati, it
seems to me that they must have become dissatisfied. Bahuke disvāna
vivitte āsane; They were so learned, such brilliant speakers! Te
cittakathā bahussutā, Where have these disciples of Gotama gone?” Kome
You keep examining suttas as above until conclusive (if possible). In fact, the above method is the only method of understanding the True Dhamma.
SN 5.1 below is clearer:
Sensual pleasures are like swords and stakes; Sattisūlūpamā kāmā, the
aggregates are their chopping block. khandhāsaṁ adhikuṭṭanā; What you
call sensual delight Yaṁ tvaṁ kāmaratiṁ brūsi, has become no delight
for me.” arati mayha sā ahū”ti.
Based on the above, it appears "discontentment" is the most general meaning.
Again, Snp 3.2 below supports "discontent":
Sensual pleasures are your first army, Kāmā te paṭhamā senā, the
second is called discontent, Dutiyā arati vuccati; hunger and thirst
are the third, Tatiyā khuppipāsā te, and the fourth is said to be
craving. Catutthī taṇhā pavuccati. Your fifth is dullness and drowsiness, Pañcamaṁ thinamiddhaṁ te,
the sixth is said to be
cowardice, Chaṭṭhā bhīrū pavuccati; your seventh is doubt, Sattamī
vicikicchā te, contempt and obstinacy are your eighth. Makkho thambho
Again, AN 1.13 below clearly points to "discontentment" or "lack of joy":
Mendicants, I do not see a single thing that gives rise to dullness
and drowsiness, or, when they have arisen, makes them increase and
grow like discontent, sloth, yawning, sleepiness after eating, and
mental sluggishness. “Nāhaṁ, bhikkhave, aññaṁ ekadhammampi
samanupassāmi yena anuppannaṁ vā thinamiddhaṁ uppajjati uppannaṁ vā
thinamiddhaṁ bhiyyobhāvāya vepullāya saṁvattati yathayidaṁ, bhikkhave,
arati tandī vijambhitā bhattasammado cetaso ca līnattaṁ.
The above sutta concludes my search.
In summary, while resentment can be a form of discontentment, it appears the general meaning of 'arati' is 'discontentment' or 'lack of joy/appreciation'.