The Latin noun lupus/-pi meant wolf. It is kindred with ancient Greek λύκος (lukos).
—Cf. lycanthrope, which originally designated a person who believes that he or she is a wolf, and which, via the modern Latin noun lycanthrōpus, is from Greek λυκάνθρωπος (lukanthropos), literally wolf-man, from λύκος and ἄνθρωπος (anthropos), man.

The Latin lupus has sometimes been used in English in the sense of wolf; for instance, a Scottish satirical poem composed in 1583 thus begins:

All fayᵗfull brether that on the Lord dependis,
Mark weill this schedule that I have send you heir,
Pestiferus prelatis that Papistrie pretendis,
Sic dewils but dout sall in oʳ dayis appeir;
Yit God forwairns you, be the weidis they weir,
To ken the lupus in a lamb skyn lappit.
     translation:
All faithful brethren that on the Lord depend,
Take good note of the missive that I have sent you here,
Pernicious prelates that papistry declares,
Such devils beyond doubt shall in our days appear;
Yet God forbids you, by the garments they wear,
To recognise the wolf in a lamb’s skin clothed.

This is a reference to the gospel of Matthew, 7:15:

(Revised Standard Version)
Beware of false prophets, who come to you in sheep’s clothing but inwardly are ravenous wolves.

Since at least around 1400, lupus has been applied to any of various ulcerative skin diseases. The probable reason for this use was explained by the medical writer Philip Barrough in The methode of phisicke conteyning the causes, signes, and cures of invvard diseases in mans body from the head to the foote. Whereunto is added, the forme and rule of making remedies and medicines, which our phisitians commonly vse at this day, with the proportion, quantitie, & names of ech [sic] medicine (1583):

Lupus morbus.
Lupus is a malignant vlcer quickly consuming the neither partes, but specially annoying the thighes and legges, and it is very hungry like vnto a woulfe (wherof it seemeth to receiue this title) eating vp the flesh that ly next vnto it, which euill without doubt is of the kind of Phagedænæ.

Similarly, cancer is a Latin noun which literally meant a crab, and figuratively a crawling, eating tumour. It is related to Greek καρκίνος (karkinos), of same meanings. According to the Greek physician and surgeon Paulus Aegineta (circa 625-circa 690) in Epitomēs iatrikēs biblio hepta (Latin Epitomae medicae libri septem – Medical Compendium in Seven Books), the tumour was so called because the swollen veins surrounding the part affected bore a resemblance to the limbs of a crab. This explanation was widely cited by medieval writers.