The only free and comprehensive online etymological dictionary of the Spanish language
camisa f. (Noun) "shirt"

Very late 9th cent. Borrowed from Late Latin camisa 'id.,' from Latin camisia 'id.' Probably borrowed from a non-Indo-European language with cognates in Germanic.

Germanic: West Germanic: Old High German hemidi, Old English hemeþe
campar (Verb) "to stand out"

16th cent. From campo.

Romance: Western Vulgar Latin: Asturian camín, Portuguese caminho, Galician camiño, Catalan camí, French chemin, Italian cammino

Probably derived from the military sense of campo "field," where one excels in the field of battle (compare campeón).
campeón (Noun) "champion"

Late 16th cent. borrowing from Italian campione 'id.,' itself borrowed from Late Latin campionem, accusative of campio "fighter." From Latin campus "field" (see campo).
campo m. (Noun) "countryside," "field"

10th cent. From Latin campus "field" but metaphorically a field (for an event like a battle or debate). A similar development occurs in English phrases like "playing field" or "battlefield." From Proto-Italic *kampo- 'field.' Of unknown origin, probably a substrate source.

The original sense in Latin of a treeless field is even better preserved in campa "empty field." Also the origin of myriad toponyms through Spain and the Spanish-speaking world. As a surname in Campo, Campos, del Campo, Cámpiz, it was given to families known for their homes in the countryside.

Romance: Western Vulgar Latin: Asturian campu, Portuguese campo, Galician campo, Catalan camp, French champ, Italian camp; Eastern Vulgar Latin: Aromanian cãmpu, Romanian câmp; Sardinian: campu

Germanic: East Germanic: Gothic hamfs "mutilated;" West Germanic: Old High German hamf "maimed," Old English hāf 'id.'

Balto-Slavic: Baltic: Lithuanian kam̃pas "corner," kum̃pas "curved," Latvian kùmpt "to be bent;" Slavic: Old Church Slavonic kǫtъ "corner"

Hellenic: Ancient Greek καμπή (kampé) "bow"

Related to Spanish campeón as a champion fighter was the foremost on the field of battle.
canal m. (Noun) "channel;" "canal"

12th cent. From Latin canalis "pipe," "ditch." Probably from canna "reed," itself borrowed from Ancient Greek κάννα ‎(kánna) 'id.' Borrowed from Assyrian qanū 'id.' Ultimately borrowed from Sumerian gin 'id.'

Also the origin of the surname de la Canal.
canción f. (Noun) "song"

13th cent. From Latin cantionem, accusative of cantio 'id.' From cantare "to sing" (see cantar).

Romance: Western Vulgar Latin: Asturian canción, Portuguese canção, Galician canción, Catalan cançó, French chanson, Italian canzone; Sardinian: cancione
cansado (Adjective) "tired"

Late 15th cent. From the past participle of cansar.
cansar (Verb) "to tire"

11th cent. From Latin campsare "to avoid." Probably borrowed from Ancient Greek κάμψαι (kámpsai) "to be bent," "to be sailed around;" the aorist infinitive of κάμπτειν (kámptein) "to bend," "to curve." Of unknown origin, probably borrowed from a non-Indo-European language. Probably from the same origin of campo.

Romance: Western Vulgar Latin: Asturian cansar, Portuguese cansar, Galician cansar, Catalan cansar, Italian cansare

Penny (2002) notes that cansar is a particularly interesting archaism in Spanish. Because the Romans entered the Iberian peninsula and began the process of Latinization at such an early date (~3rd cent. BCE), the Latin dialect of the peninsula inherited a number of archaic vocabulary terms. Cansar is one such item, not found in Latin literature after the 2nd cent. BCE but evidently preserved in the dialect of Latin to become Spanish.
canso (Adjective) "tired"

13th cent. From Vulgar Latin *campsus 'id.,' from Latin campsare "to avoid" (see cansar).
cantar (Verb) "to sing"

10th cent. From Latin cantare "to sing," "to chant." From Latin canare "to sing" and frequentive suffix -tare (see note under faltar for origin). From Proto-Italic *kan-e(je)- 'id.' From Proto-Indo-European *kh2n-e- 'id.'

Romance: Western Vulgar Latin: Asturian cantar, Portuguese cantar, Galician cantar, Catalan cançó, French chanter, Italian cantare; Eastern Vulgar Latin: Aromanian cãntu, Romanian cânta; Sardinian: cantari

Originally canare meant "to sing" while cantare, with -tare added, was more forceful. Over time the impact of cantare was lost and began to match the meaning of canare. Thus, canare was replaced by cantare. When later speakers wanted to indicate force and frequency to the verb, they once again added -tare to cantare to form cantitare - unaware that their ancestors had created cantare from canare to fill that purpose. Cantitare has not survived in Spanish.