Seeing

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Old English sēon, of Germanic origin; related to Dutch zien and German sehen, perhaps from an Indo-European root shared by Latin sequi ‘follow’.

wiktionary

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see +‎  -ing

Probably an elision of "seeing that" or "seeing as".

etymonline

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seeing (adj.)

c. 1300, present-participle adjective from see (v.). Seeing Eye dog first attested 1929, American English, trademarked by Seeing Eye Inc. of New Jersey.