Simple past tense and past participle of jam-pack.(verb)
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Use "jam-packed" in a sentence
"I understand all the hospitals and clinics were jam-packed for a day or 2 when the frightening news came out, but that was very temporary."
"One night I saw this train with black cotton workers coming back from the South, jam-packed."
"The small shop is jam-packed with clothing, ranging from lace prairie dresses from the 1910s to 1980s couture, worn by mannequins with spooky cat-head masks."