An archaic or poetic past tense form of 'cross,' meaning to move across or traverse something.
Old English 'crosian' became 'cross' in Middle English, and 'crost' is an archaic simple past form, now obsolete in modern usage.
Reading old poetry, you'll see 'crost' and 'blest' and 'passed' thrown around—poets used these shortened past tenses to make their meter fit the rhythm, which is why Shakespeare has so many weird-looking verb forms.
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