Short answers, pulled from the story.
Lewis Carroll introduced the concept of portmanteau as a linguistic term in his 1871 book Through the Looking-Glass. The word portmanteau was not originally a linguistic term but a piece of luggage before this literary invention.
The word portmanteau comes from the French words porter meaning to carry and manteau meaning cloak. By the 16th century it referred to an officer who carried the mantle of a person in a high position and by the 17th century it described a clothes rack or a case for carrying clothing.
Lewis Carroll defined portmanteau as a process of taking two words and making up one's mind to say both resulting in a single word like frumious from fuming and furious. This method allowed for the creation of entirely new concepts without the need for lengthy phrases.
Linguists classify portmanteaus into morphotactic morphological and morphosemantic categories. These classifications include total blends partial blends overlapping blends non-overlapping blends attributive blends and coordinate blends.
The word brunch was introduced in Punch in 1896 as a portmanteau of breakfast and lunch. This type of blend is used to create a new identity for a concept reflecting the merging of two distinct elements into a single entity.