Origin: bef. 1000; ME
prati(
e),
pratte, prettie cunning, gallant, fine, handsome, pretty; OE
prættig, prettī cunning, deriv. of
prǣtt a trick, wile (c. D
part, pret trick, prank, ON
prettr trick,
prettugr tricky)
Related forms: pret⋅ti⋅ly, adverb
pret⋅ti⋅ness, noun
pret⋅ty⋅ish, adjective
Synonyms:1. See beautiful. 2–4. pleasant.
10. somewhat.
Antonyms:
1. ugly.
Usage note:
The qualifying adverb pretty, meaning “fairly or moderately” has been in general use since the late 16th century. Although most common in informal speech and writing, it is far from restricted to them, and often is less stilted than alternatives such as relatively, moderately, and quite.
[prit-ee] 
adjective, -ti⋅er, -ti⋅est, noun, plural -ties, adverb, verb, -tied, -ty⋅ing.