Complimentary

[Bert]

I wonder how the word "compliment", meaning praise, developed into "complimentary" meaning something given for no charge.

[Quizmonster]

The verb, to compliment, in the 1600s meant to treat ceremoniously or with formal courteously, but quickly took on the meaning of praise as there is not a big step between the two forms of behaviour.
As the giving of gifts is frequently an element of ceremonious occasions - eg visiting heads of state are always handed something or other - the adjective, complimentary, had become used to mean 'free' in the sense of tickets etc by the 19th century.

[Quizmonster]

Oops! Courtesy...got carried away with my ouslies!

[nightmare]

Quizmonster,
at least it is not as painful as being carried away BY your ouslies !

[Quizmonster]

Quite, N-M...that sounds rather like being picked up by the fuzz!

[jno]

formal gifts are still sometimes labelled "with the compliments of the management" or something like that... the subtext is that they are giving you this to show what a nice person they think you are.