dogface (n.)

"quadruped of the genus Canis," Old English docga, a late, rare word, used in at least one Middle English source in reference specifically to a powerful breed of canine; other early Middle English uses tend to be depreciatory or abusive. Its origin remains one of the great mysteries of English etymology.

The word forced out Old English hund (the general Germanic and Indo-European word, from root from PIE root *kwon-) by 16c. and subsequently was picked up in many continental languages (French dogue (16c.), Danish dogge, German Dogge (16c.). The common Spanish word for "dog," perro, also is a mystery word of unknown origin, perhaps from Iberian. A group of Slavic "dog" words (Old Church Slavonic pisu, Polish pies, Serbo-Croatian pas) likewise is of unknown origin. 

In reference to persons, by c. 1200 in abuse or contempt as "a mean, worthless fellow, currish, sneaking scoundrel." Playfully abusive sense of "rakish man," especially if young, "a sport, a gallant" is from 1610s. Slang meaning "ugly woman" is from 1930s; that of "sexually aggressive man" is from 1950s.  

Many expressions — a dog's life (c. 1600), go to the dogs (1610s), dog-cheap (1520s), etc. — reflect the earlier hard use of the animals as hunting accessories, not pets. In ancient times, "the dog" was the worst throw in dice (attested in Greek, Latin, and Sanskrit, where the word for "the lucky player" was literally "the dog-killer"), which plausibly explains the Greek word for "danger," kindynos, which appears to be "play the dog" (but Beekes is against this).

Notwithstanding, as a dog hath a day, so may I perchance have time to declare it in deeds. [Princess Elizabeth, 1550]

Meaning "something poor or mediocre, a failure" is by 1936 in U.S. slang. From late 14c. as the name for a heavy metal clamp of some kind. Dog's age "a long time" is by 1836. Adjectival phrase dog-eat-dog "ruthlessly competitive" is by 1850s. Phrase put on the dog "get dressed up" (1934) may be from comparison of dog collars to the stiff stand-up shirt collars that in the 1890s were the height of male fashion (and were known as dog-collars from at least 1883).

And Caesar's spirit, ranging for revenge,

With Ate by his side come hot from Hell,

Shall in these confines with a monarch's voice

Cry Havoc! and let slip the dogs of war;

[Shakespeare, "Julius Caesar"]

c. 1300, "the human face, a face; facial appearance or expression; likeness, image," from Old French face "face, countenance, look, appearance" (12c.), from Vulgar Latin *facia (source also of Italian faccia), from Latin facies "appearance, form, figure," and secondarily "visage, countenance," which probably is literally "form imposed on something" and related to facere "to make" (from PIE root *dhe- "to set, put").

Replaced Old English andwlita "face, countenance" (from root of wlitan "to see, look") and ansyn, ansien, the usual word (from the root of seon "see"). Words for "face" in Indo-European commonly are based on the notion of "appearance, look," and are mostly derivatives from verbs for "to see, look" (as with the Old English words, Greek prosopon, literally "toward-look," Lithuanian veidas, from root *weid- "to see," etc.). But in some cases, as here, the word for "face" means "form, shape." In French, the use of face for "front of the head" was given up 17c. and replaced by visage (older vis), from Latin visus "sight."

From late 14c. as "outward appearance (as contrasted to some other reality);" also from late 14c. as "forward part or front of anything;" also "surface (of the earth or sea), extent (of a city)." Typographical sense of "part of the type which forms the letter" is from 1680s.

Whan she cometh hoom, she raumpeth in my face And crieth 'false coward.' [Chaucer, "Monk's Tale"]

Face to face is from mid-14c. Face time is attested from 1990. To lose face "lose prestige" (1835), is from Chinese tu lien; hence also save face (1898; see save). To show (one's) face "make or put in an appearance" is from mid-14c. (shewen the face). To make a face "change the appearance of the face in disgust, mockery, etc." is from 1560s. Two faces under one hood as a figure of duplicity is attested from mid-15c.

Two fases in a hode is neuer to tryst. ["Awake lordes," 1460]