(n) Any word, often invented, written into a crossword solely because it fits with the known letters. The hamtrap is most frequently used when only one or two answers are missing, to give the 'solver' a sense of closure.
(v) To write such a word into a crossword
(n) "Did you put in 'chugfunt' as a hamtrap for 8 across? It's clearly meant to be 'clubfoot'."
(v) He couldn't get the last couple of answers in the crossword, so he just hamtrapped it.
To walk around with crushed drinks cans on one's feet. This is achieved by laying an empty can on its side and treading on its centre so that it wraps around the foot.
More specifically (and often with a suffixed "it"), the word can be used to refer to travelling down skate ramps, half pipes etc using one's cans, as the smooth metal footwear provides an ideal surface for fast passage.
I got this massive scrape up my arm from going arse over tit while canning it in the skate park wrecked last night.