Climbing or ascending, or the present participle of the verb 'blimb' (a rare variant of climb).
From Middle English 'climben,' the word 'blimb' appears as a variant pronunciation/spelling, possibly influenced by Scandinavian languages, with '-ing' added for present participle.
The word 'blimb' is so archaic that dictionaries barely record it, yet it shows how English had multiple pronunciations of 'climb' that almost became permanent alternatives.
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