British past tense of caucus, using the double-s spelling convention common in British English before adding -ed.
From caucus with British spelling doubling the final consonant (caucuss-) before adding -ed. British English often doubles final consonants differently than American English, creating this variant form.
This is a fun example of how American and British English diverged—while Americans write 'caucused,' the British would say 'caucussed,' turning one historical word into two orthographic cousins.
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