What's the practice for short-forming or nicknaming words called?

Question

Is there any term for the habit of playing around with words, or even names, and nickname them? Like 'No' becoming 'nopes', 'whatever' becoming 'tevs', milky-wilky etc. This happens a lot with cricket teams, who keep nicknaming people - Wilkinson becomes Willy or Wilks, Hogg becomes Hoggy (though it's longer).

Answer 1

'Nicknaming' specifically for names.

Other words you can use: 'abbreviation' or 'to abbreviate' and 'dimimutive'

di·min·u·tive (adjective) /diˈminyətiv/ 

Extremely or unusually small - a diminutive figure dressed in black

(of a word, name, or suffix) Implying smallness, either actual or imputed in token of affection, scorn, etc., (e.g., teeny, -let, -kins)