Definition of well in in English:

well in

Pronunciation /ˌwɛl ˈɪn/

adverb

informal
  • 1British, Irish In the position of having established a good relationship with someone; on good terms.

    Originally construed as well qualifying in with.

  • 2In a situation or position where one's sexual or romantic advances are very likely to be successful.

  • 3Horse Racing
    With a very good chance; with favourable odds.

  • 4Australian So as to be well established; in favourable or comfortable circumstances; specifically (Australian) = "well off".

    Formerly also: in profitable engagement in speculation.

Origin

Late 18th century; earliest use found in Peter Beckford (1740–1811), dog breeder and writer on hunting. From well + in.