adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga (cf. German -ig), cognate with Greek -ikos, Latin -icus.
suffix in pet proper names (e.g. Johnny, Kitty), first recorded in Scottish, c.1400; became frequent in English 15c.-16c. Extension to surnames seems to date from c.1940. Use with common nouns seems to have begun in Scottish with laddie (1546) and become popular in English due to Burns' poems, but the same formation appears to be represented much earlier in baby and puppy.