Where does the “-bie” in newbie originate. mw just says: “Etymology: irregular from new”

It’s not known for sure. Here’s what OED has for the etymology:

[Origin uncertain. Perh. alteration of NEWIE n., with abritrary insertion of -b- (perh. cf. FREEBIE n.); or perh. alteration of NEW BOY n. after -Y6.
It seems unlikely that there is any connection with formations in -BY 2, which are much earlier in date.]

Aren’t there several terms like this?  Military, Police or firefighter word is ”probie” which I know from the TV show NCIS.

One on probation is a “probie” and one who is new is a “newbie.” other diminutives such as “swabbie” (one who swabs a deck?), “freebie”, “cabbie” and the like.

One on probation is a “probie” and one who is new is a “newbie.” other diminutives such as “swabbie” (one who swabs a deck?), “freebie”, “cabbie” and the like.

But the b is present in the root-word for probie, swabbie, and cabbie: they’re formed simply by the addition of -ie, which is typical of English diminutives (and similar derivatives), to the original word or its stem.  In freebie and newbie the b is intrusive, and its origin is somewhat mysterious.

OBTW, old discussions:
newbie
freebie

Maybe the cartoon Fat Albert started it. The little kid put “b’s” into almost every word. Just kidding, I think. :}

Cassell’s suggests the “new boy” explaination with a “?”.