Noun

(en-noun)

The amount that will fit in a mouth.

* He swallowed a mouthful of sea water when he fell in.

(slang) Quite a bit.

* {{quote-book

, year=1960 , author= , title=(Jeeves in the Offing) , section=chapter VII , passage=“Unquestionably his metabolism is unduly susceptible to stresses resulting from the interaction of external excitations,” he said, and Bobbie patted him on the shoulder in a maternal sort of way, a thing I wouldn't have cared to do myself though our relations were, as I have indicated, more cordial than they had been at one time, and told him he had said a mouthful .}}

Something difficult to pronounce or say.

* "She sells sea shells" is a bit of a mouthful to say.

* {{quote-book

, year=1960 , author= , title=(Jeeves in the Offing) , section=chapter X , passage=“Yes, you may leave this little matter entirely to me, Mr Wooster.” “I wish you'd call me Bertie.” “Certainly, certainly.” “And might I call you Roderick?” “I shall be delighted.” “Or Roddy? Roderick's rather a mouthful .” “Whichever you prefer.”}}

* 2010 , Alexander Irvine, Iron Man 2: The Junior Novel , page 77

"Tony, I'm the executive director of S.H.I.E.L.D., the Strategic Homeland Intelligence, Enforcement, and Logistics Division," explained Fury.
Tony nodded. "Want a tip? Fire your namer of things, because that's a mouthful ."

A tirade of abusive language (especially in the term "give someone a mouthful")