‘And thou wilt come to the isle Thrinacia. There in great numbers feed the kine of Helios and his goodly flocks, seven herds of kine and as many fair flocks of sheep, and fifty in each.’’   Odyssey 12.127ff.  (online text: Eng.Grk.)
[here and below quotes are selective; follow links for complete passages]

Scholarship has long assumed that Trinakria (Τρινακρία) is related to Homer’s Thrinacia (Θρινακίη). It is widely suspected that the name is derived from treis arkai (τρεῖς ἄκραι), and was an erroneous ‘correction’ of the name Thrinacia, owing to increased awareness of Sicily’s roughly triangular shape since the time of Homer.

 Sicania Od. 24.307

Ancient Localization

Thucydides 6.2.2

“It was from them [Sicanians] that the island, before called Trinacaria [Trinakria], took its name of Sicania, and to the present day they inhabit the west of Sicily.”
(online text: Eng., Grk.)

Virgil, Aeneid 3.429ff.

(Helenus, giving directions around Sicily):  “Better by far to round the distant goal/of the Trinacrian headlands, veering wide/from thy true course, than ever thou shouldst see/that shapeless Scylla in her vaulted cave,/where grim rocks echo her dark sea-dogs’ roar….So shalt thou, triumphing,/to Italy be sped, and leave behind Trinacria.”
(online text: Eng., Lat.)

Strabo, Geography 6.2.1

“Sicily is triangular in form, and on this account was at first called Trinacria, but afterwards the name was softened and it was changed into Thrinacia. Three low headlands bound the figure: Pelorias is the name of that towards Cænys and the Columna Rheginorum which forms the strait; Pachynus2 is that which stretches towards the east, and is washed by the Sea of Sicily, looking towards the Peloponnesus and in the direction of the passage to Crete; the third is Lilybæum, and is next to Africa, looking towards that region and the setting of the sun in winter.”
(online text: Eng., Grk.)

Justin, Epitome of Pompeius Trogus 4.2

“At first Sicily had the name of Trinacria; afterwards it was called Sicania. It was originally the abode of the Cyclops…”
(online text: Eng.Lat.)

Pliny, Natural History 3.8

“But more celebrated than all is Sicily, called Sicania by Thucydides, and by many writers Trinacria or Trinacia, from its triangular appearance.”
(online text: Eng.Lat.)