Proper noun
(Greek mythology) One of the Nereids; the mother of Achilles
(astronomy) 17 Thetis, one of the main belt asteroids.
Source: en.wiktionary.orgLong time has Thetis been scanning every corner with silent glance. Statius
The Nereids, swimming in from all directions, met them here, and Lady Thetis coming up astern laid her hand on the blade of the steering-oar to guide them through the Wandering Rocks. Apollonius of Rhodes
You can't love Thetis and Galatea at the same time. Latin Proverb
As an infant, Archilles was plunged in the River Styx by his mother Thetis (also see 17 Thetis), thus rendering his body invulnerable excepting the heel by which he was held. Source: Internet
At this same time, burning with rage over Agamemnon's theft, Achilles prays to Thetis to convince Zeus to help the Trojans gain ground in the war, so that he may regain his honor. Source: Internet
A number of sources credit Thetis with attempting to make Achilles immortal when he was an infant. Source: Internet