Spunk

google

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mid 16th century (in the sense ‘a spark, vestige’): of unknown origin; perhaps a blend of spark1 and obsolete funk ‘spark’.

wiktionary

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1530, blend of spark +‎ funk(obsolete, “spark”). Also, merging with spunck, 1582, ultimately from Middle Irish sponc, from Latin spongia(“sponge”).

Funk(“spark, touchwood”) is from Middle English funke,  fonke(“spark”), from Old English *funce(“spark”),  *fanca, from Proto-Germanic *funkô,  *fankô(“spark”), from Proto-Indo-European *(s)peng-(“to shine”), and is akin to Middle Low German funke,  fanke(“spark”), Middle Dutch vonke(“spark”), Old High German funcho,  funko(“spark”), German Funke(“spark”). 

etymonline

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spunk (n.)

1530s, "a spark," Scottish, from Gaelic spong "tinder, pith, sponge," from Latin spongia (see sponge (n.)). The sense of "courage, pluck, mettle" is first attested 1773. A similar sense evolution took place in cognate Irish sponnc "sponge, tinder, spark; courage, spunk." Vulgar slang sense of "seminal fluid" is recorded from c. 1888.