From Porniki

fuck

to have sex.

from wikipedia:

Fuck is an English word which, when used literally as a verb, means "to engage in sexual intercourse". It is generally considered to be an offensive profanity. Its origins may be Germanic, akin to the synonymous German ficken, which had the original meaning, "to strike".

It is unclear whether the word has always been considered vulgar, and if not, when it first started to be considered vulgar. Some evidence indicates that in some English-speaking locales it was considered acceptable as late as the 17th century meaning "to strike" or "to penetrate."[1] Other evidence indicates that it may have become vulgar as early as the 16th century in England, although neither set of evidence is inherently contradictory to the other, since many words have multiple connotations. The etymology of the word is uncertain (see below).

In contemporary usage, the versatility of the word is such that it can be used as a transitive verb (he fucks her), intransitive verb (she fucks quite often), noun (he is a silly fuck), adverb (this car won't fucking drive), adverb enhancing an adjective (his dog is fucking crazy), interjection (where the fuck did this come from?), or an exclamation (Fuck!). Fuck is also one of the few words in English commonly used as an infix, as in absofuckinglutely, infuckingcredible, and congratufuckinglations along with several other expletive infixes.

Fuck. (2006, November 30). In Wikipedia, The Free Encyclopedia. Retrieved 05:30, December 2, 2006, from http://en.wikipedia.org/w/index.php?title=Fuck&oldid=91085116