/ ˌtʃɒk ə ˈblɒk; NAmE ˌtʃɑːk ə ˈblɑːk/ (also chocka / ˈtʃɒkə; NAmE ˈtʃɑːkə/) adjective
[ not before noun ] chock-a-block (with sth/sb) ( BrE , informal ) very full of things or people pressed close together :
The shelves were chock-a-block with ornaments.
It was chock-a-block in town today (= full of people) .
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WORD ORIGIN
mid 19th cent. (originally in nautical use, with reference to tackle having the two blocks run close together): from chock (in chock-full ) and block .